| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> |
| <html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Git User Manual</title><link rel="stylesheet" type="text/css" href="docbook-xsl.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book"><div class="titlepage"><div><div><h1 class="title"><a name="idm1"></a>Git User Manual</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="preface"><a href="#idm4"></a></span></dt><dt><span class="chapter"><a href="#repositories-and-branches">1. Repositories and Branches</a></span></dt><dd><dl><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a Git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></dd><dt><span class="chapter"><a href="#exploring-git-history">2. Exploring Git history</a></span></dt><dd><dl><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-commits-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#Developing-With-git">3. Developing with Git</a></span></dt><dd><dl><dt><span class="section"><a href="#telling-git-your-name">Telling Git your name</a></span></dt><dt><span class="section"><a href="#creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">How to make a commit</a></span></dt><dt><span class="section"><a href="#creating-good-commit-messages">Creating good commit messages</a></span></dt><dt><span class="section"><a href="#ignoring-files">Ignoring files</a></span></dt><dt><span class="section"><a href="#how-to-merge">How to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dd><dl><dt><span class="section"><a href="#conflict-resolution">Getting conflict-resolution help during a merge</a></span></dt></dl></dd><dt><span class="section"><a href="#undoing-a-merge">Undoing a merge</a></span></dt><dt><span class="section"><a href="#fast-forwards">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#fixing-mistakes">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#reverting-a-commit">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#fixing-a-mistake-by-rewriting-history">Fixing a mistake by rewriting history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</a></span></dt><dt><span class="section"><a href="#interrupted-work">Temporarily setting aside work in progress</a></span></dt></dl></dd><dt><span class="section"><a href="#ensuring-good-performance">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#ensuring-reliability">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#checking-for-corruption">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#recovering-lost-changes">Recovering lost changes</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#sharing-development">4. Sharing development with others</a></span></dt><dd><dl><dt><span class="section"><a href="#getting-updates-With-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#submitting-patches">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#importing-patches">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#public-repositories">Public Git repositories</a></span></dt><dd><dl><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a Git repository via the Git protocol</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via HTTP</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#forcing-push">What to do when a push fails</a></span></dt><dt><span class="section"><a href="#setting-up-a-shared-repository">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#setting-up-gitweb">Allowing web browsing of a repository</a></span></dt></dl></dd><dt><span class="section"><a href="#how-to-get-a-git-repository-with-minimal-history">How to get a Git repository with minimal history</a></span></dt><dt><span class="section"><a href="#sharing-development-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#maintaining-topic-branches">Maintaining topic branches for a Linux subsystem maintainer</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#cleaning-up-history">5. Rewriting history and maintaining patch series</a></span></dt><dd><dl><dt><span class="section"><a href="#patch-series">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#using-git-rebase">Keeping a patch series up to date using git rebase</a></span></dt><dt><span class="section"><a href="#rewriting-one-commit">Rewriting a single commit</a></span></dt><dt><span class="section"><a href="#reordering-patch-series">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#interactive-rebase">Using interactive rebases</a></span></dt><dt><span class="section"><a href="#patch-series-tools">Other tools</a></span></dt><dt><span class="section"><a href="#problems-With-rewriting-history">Problems with rewriting history</a></span></dt><dt><span class="section"><a href="#bisect-merges">Why bisecting merge commits can be harder than bisecting linear history</a></span></dt></dl></dd><dt><span class="chapter"><a href="#advanced-branch-management">6. Advanced branch management</a></span></dt><dd><dl><dt><span class="section"><a href="#fetching-individual-branches">Fetching individual branches</a></span></dt><dt><span class="section"><a href="#fetch-fast-forwards">git fetch and fast-forwards</a></span></dt><dt><span class="section"><a href="#forcing-fetch">Forcing git fetch to do non-fast-forward updates</a></span></dt><dt><span class="section"><a href="#remote-branch-configuration">Configuring remote-tracking branches</a></span></dt></dl></dd><dt><span class="chapter"><a href="#git-concepts">7. Git concepts</a></span></dt><dd><dl><dt><span class="section"><a href="#the-object-database">The Object Database</a></span></dt><dd><dl><dt><span class="section"><a href="#commit-object">Commit Object</a></span></dt><dt><span class="section"><a href="#tree-object">Tree Object</a></span></dt><dt><span class="section"><a href="#blob-object">Blob Object</a></span></dt><dt><span class="section"><a href="#trust">Trust</a></span></dt><dt><span class="section"><a href="#tag-object">Tag Object</a></span></dt><dt><span class="section"><a href="#pack-files">How Git stores objects efficiently: pack files</a></span></dt><dt><span class="section"><a href="#dangling-objects">Dangling objects</a></span></dt><dt><span class="section"><a href="#recovering-from-repository-corruption">Recovering from repository corruption</a></span></dt></dl></dd><dt><span class="section"><a href="#the-index">The index</a></span></dt></dl></dd><dt><span class="chapter"><a href="#submodules">8. Submodules</a></span></dt><dd><dl><dt><span class="section"><a href="#_pitfalls_with_submodules">Pitfalls with submodules</a></span></dt></dl></dd><dt><span class="chapter"><a href="#low-level-operations">9. Low-level Git operations</a></span></dt><dd><dl><dt><span class="section"><a href="#object-manipulation">Object access and manipulation</a></span></dt><dt><span class="section"><a href="#the-workflow">The Workflow</a></span></dt><dd><dl><dt><span class="section"><a href="#working-directory-to-index">working directory → index</a></span></dt><dt><span class="section"><a href="#index-to-object-database">index → object database</a></span></dt><dt><span class="section"><a href="#object-database-to-index">object database → index</a></span></dt><dt><span class="section"><a href="#index-to-working-directory">index → working directory</a></span></dt><dt><span class="section"><a href="#tying-it-all-together">Tying it all together</a></span></dt></dl></dd><dt><span class="section"><a href="#examining-the-data">Examining the data</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees">Merging multiple trees</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees-2">Merging multiple trees, continued</a></span></dt></dl></dd><dt><span class="chapter"><a href="#hacking-git">10. Hacking Git</a></span></dt><dd><dl><dt><span class="section"><a href="#object-details">Object storage format</a></span></dt><dt><span class="section"><a href="#birdview-on-the-source-code">A birds-eye view of Git’s source code</a></span></dt></dl></dd><dt><span class="chapter"><a href="#glossary">11. Git Glossary</a></span></dt><dd><dl><dt><span class="section"><a href="#git-explained">Git explained</a></span></dt></dl></dd><dt><span class="appendix"><a href="#git-quick-start">A. Git Quick Reference</a></span></dt><dd><dl><dt><span class="section"><a href="#quick-creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#managing-branches">Managing branches</a></span></dt><dt><span class="section"><a href="#exploring-history">Exploring history</a></span></dt><dt><span class="section"><a href="#making-changes">Making changes</a></span></dt><dt><span class="section"><a href="#merging">Merging</a></span></dt><dt><span class="section"><a href="#sharing-your-changes">Sharing your changes</a></span></dt><dt><span class="section"><a href="#repository-maintenance">Repository maintenance</a></span></dt></dl></dd><dt><span class="appendix"><a href="#todo">B. Notes and todo list for this manual</a></span></dt><dd><dl><dt><span class="section"><a href="#todo-list">Todo list</a></span></dt></dl></dd></dl></div><div class="preface"><div class="titlepage"><div><div><h1 class="title"><a name="idm4"></a></h1></div></div></div><p>Git is a fast distributed revision control system.</p><p>This manual is designed to be readable by someone with basic UNIX |
| command-line skills, but no previous knowledge of Git.</p><p><a class="xref" href="#repositories-and-branches" title="Chapter 1. Repositories and Branches">Chapter 1, <i>Repositories and Branches</i></a> and <a class="xref" href="#exploring-git-history" title="Chapter 2. Exploring Git history">Chapter 2, <i>Exploring Git history</i></a> explain how |
| to fetch and study a project using git—read these chapters to learn how |
| to build and test a particular version of a software project, search for |
| regressions, and so on.</p><p>People needing to do actual development will also want to read |
| <a class="xref" href="#Developing-With-git" title="Chapter 3. Developing with Git">Chapter 3, <i>Developing with Git</i></a> and <a class="xref" href="#sharing-development" title="Chapter 4. Sharing development with others">Chapter 4, <i>Sharing development with others</i></a>.</p><p>Further chapters cover more specialized topics.</p><p>Comprehensive reference documentation is available through the man |
| pages, or <a class="ulink" href="git-help.html" target="_top">git-help(1)</a> command. For example, for the command |
| <code class="literal">git clone <repo></code>, you can either use:</p><pre class="literallayout">$ man git-clone</pre><p>or:</p><pre class="literallayout">$ git help clone</pre><p>With the latter, you can use the manual viewer of your choice; see |
| <a class="ulink" href="git-help.html" target="_top">git-help(1)</a> for more information.</p><p>See also <a class="xref" href="#git-quick-start" title="Appendix A. Git Quick Reference">Appendix A, <i>Git Quick Reference</i></a> for a brief overview of Git commands, |
| without any explanation.</p><p>Finally, see <a class="xref" href="#todo" title="Appendix B. Notes and todo list for this manual">Appendix B, <i>Notes and todo list for this manual</i></a> for ways that you can help make this manual more |
| complete.</p></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="repositories-and-branches"></a>Chapter 1. Repositories and Branches</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a Git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-get-a-git-repository"></a>How to get a Git repository</h2></div></div></div><p>It will be useful to have a Git repository to experiment with as you |
| read this manual.</p><p>The best way to get one is by using the <a class="ulink" href="git-clone.html" target="_top">git-clone(1)</a> command to |
| download a copy of an existing repository. If you don’t already have a |
| project in mind, here are some interesting examples:</p><pre class="literallayout"> # Git itself (approx. 40MB download): |
| $ git clone git://git.kernel.org/pub/scm/git/git.git |
| # the Linux kernel (approx. 640MB download): |
| $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git</pre><p>The initial clone may be time-consuming for a large project, but you |
| will only need to clone once.</p><p>The clone command creates a new directory named after the project |
| (<code class="literal">git</code> or <code class="literal">linux</code> in the examples above). After you cd into this |
| directory, you will see that it contains a copy of the project files, |
| called the <a class="link" href="#def_working_tree">working tree</a>, together with a special |
| top-level directory named <code class="literal">.git</code>, which contains all the information |
| about the history of the project.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-check-out"></a>How to check out a different version of a project</h2></div></div></div><p>Git is best thought of as a tool for storing the history of a collection |
| of files. It stores the history as a compressed collection of |
| interrelated snapshots of the project’s contents. In Git each such |
| version is called a <a class="link" href="#def_commit">commit</a>.</p><p>Those snapshots aren’t necessarily all arranged in a single line from |
| oldest to newest; instead, work may simultaneously proceed along |
| parallel lines of development, called <a class="link" href="#def_branch">branches</a>, which may |
| merge and diverge.</p><p>A single Git repository can track development on multiple branches. It |
| does this by keeping a list of <a class="link" href="#def_head">heads</a> which reference the |
| latest commit on each branch; the <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> command shows |
| you the list of branch heads:</p><pre class="literallayout">$ git branch |
| * master</pre><p>A freshly cloned repository contains a single branch head, by default |
| named "master", with the working directory initialized to the state of |
| the project referred to by that branch head.</p><p>Most projects also use <a class="link" href="#def_tag">tags</a>. Tags, like heads, are |
| references into the project’s history, and can be listed using the |
| <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> command:</p><pre class="literallayout">$ git tag -l |
| v2.6.11 |
| v2.6.11-tree |
| v2.6.12 |
| v2.6.12-rc2 |
| v2.6.12-rc3 |
| v2.6.12-rc4 |
| v2.6.12-rc5 |
| v2.6.12-rc6 |
| v2.6.13 |
| ...</pre><p>Tags are expected to always point at the same version of a project, |
| while heads are expected to advance as development progresses.</p><p>Create a new branch head pointing to one of these versions and check it |
| out using <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>:</p><pre class="literallayout">$ git checkout -b new v2.6.13</pre><p>The working directory then reflects the contents that the project had |
| when it was tagged v2.6.13, and <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> shows two |
| branches, with an asterisk marking the currently checked-out branch:</p><pre class="literallayout">$ git branch |
| master |
| * new</pre><p>If you decide that you’d rather see version 2.6.17, you can modify |
| the current branch to point at v2.6.17 instead, with</p><pre class="literallayout">$ git reset --hard v2.6.17</pre><p>Note that if the current branch head was your only reference to a |
| particular point in history, then resetting that branch may leave you |
| with no way to find the history it used to point to; so use this command |
| carefully.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="understanding-commits"></a>Understanding History: Commits</h2></div></div></div><p>Every change in the history of a project is represented by a commit. |
| The <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command shows the most recent commit on the |
| current branch:</p><pre class="literallayout">$ git show |
| commit 17cf781661e6d38f737f15f53ab552f1e95960d7 |
| Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)> |
| Date: Tue Apr 19 14:11:06 2005 -0700 |
| |
| Remove duplicate getenv(DB_ENVIRONMENT) call |
| |
| Noted by Tony Luck. |
| |
| diff --git a/init-db.c b/init-db.c |
| index 65898fa..b002dc6 100644 |
| --- a/init-db.c |
| +++ b/init-db.c |
| @@ -7,7 +7,7 @@ |
| |
| int main(int argc, char **argv) |
| { |
| - char *sha1_dir = getenv(DB_ENVIRONMENT), *path; |
| + char *sha1_dir, *path; |
| int len, i; |
| |
| if (mkdir(".git", 0755) < 0) {</pre><p>As you can see, a commit shows who made the latest change, what they |
| did, and why.</p><p>Every commit has a 40-hexdigit id, sometimes called the "object name" or the |
| "SHA-1 id", shown on the first line of the <code class="literal">git show</code> output. You can usually |
| refer to a commit by a shorter name, such as a tag or a branch name, but this |
| longer name can also be useful. Most importantly, it is a globally unique |
| name for this commit: so if you tell somebody else the object name (for |
| example in email), then you are guaranteed that name will refer to the same |
| commit in their repository that it does in yours (assuming their repository |
| has that commit at all). Since the object name is computed as a hash over the |
| contents of the commit, you are guaranteed that the commit can never change |
| without its name also changing.</p><p>In fact, in <a class="xref" href="#git-concepts" title="Chapter 7. Git concepts">Chapter 7, <i>Git concepts</i></a> we shall see that everything stored in Git |
| history, including file data and directory contents, is stored in an object |
| with a name that is a hash of its contents.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="understanding-reachability"></a>Understanding history: commits, parents, and reachability</h3></div></div></div><p>Every commit (except the very first commit in a project) also has a |
| parent commit which shows what happened before this commit. |
| Following the chain of parents will eventually take you back to the |
| beginning of the project.</p><p>However, the commits do not form a simple list; Git allows lines of |
| development to diverge and then reconverge, and the point where two |
| lines of development reconverge is called a "merge". The commit |
| representing a merge can therefore have more than one parent, with |
| each parent representing the most recent commit on one of the lines |
| of development leading to that point.</p><p>The best way to see how this works is using the <a class="ulink" href="gitk.html" target="_top">gitk(1)</a> |
| command; running gitk now on a Git repository and looking for merge |
| commits will help understand how Git organizes history.</p><p>In the following, we say that commit X is "reachable" from commit Y |
| if commit X is an ancestor of commit Y. Equivalently, you could say |
| that Y is a descendant of X, or that there is a chain of parents |
| leading from commit Y to commit X.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="history-diagrams"></a>Understanding history: History diagrams</h3></div></div></div><p>We will sometimes represent Git history using diagrams like the one |
| below. Commits are shown as "o", and the links between them with |
| lines drawn with - / and \. Time goes left to right:</p><pre class="literallayout"> o--o--o <-- Branch A |
| / |
| o--o--o <-- master |
| \ |
| o--o--o <-- Branch B</pre><p>If we need to talk about a particular commit, the character "o" may |
| be replaced with another letter or number.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="what-is-a-branch"></a>Understanding history: What is a branch?</h3></div></div></div><p>When we need to be precise, we will use the word "branch" to mean a line |
| of development, and "branch head" (or just "head") to mean a reference |
| to the most recent commit on a branch. In the example above, the branch |
| head named "A" is a pointer to one particular commit, but we refer to |
| the line of three commits leading up to that point as all being part of |
| "branch A".</p><p>However, when no confusion will result, we often just use the term |
| "branch" both for branches and for branch heads.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="manipulating-branches"></a>Manipulating branches</h2></div></div></div><p>Creating, deleting, and modifying branches is quick and easy; here’s |
| a summary of the commands:</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"> |
| <code class="literal">git branch</code> |
| </span></dt><dd> |
| list all branches. |
| </dd><dt><span class="term"> |
| <code class="literal">git branch <branch></code> |
| </span></dt><dd> |
| create a new branch named <code class="literal"><branch></code>, referencing the same |
| point in history as the current branch. |
| </dd><dt><span class="term"> |
| <code class="literal">git branch <branch> <start-point></code> |
| </span></dt><dd> |
| create a new branch named <code class="literal"><branch></code>, referencing |
| <code class="literal"><start-point></code>, which may be specified any way you like, |
| including using a branch name or a tag name. |
| </dd><dt><span class="term"> |
| <code class="literal">git branch -d <branch></code> |
| </span></dt><dd> |
| delete the branch <code class="literal"><branch></code>; if the branch is not fully |
| merged in its upstream branch or contained in the current branch, |
| this command will fail with a warning. |
| </dd><dt><span class="term"> |
| <code class="literal">git branch -D <branch></code> |
| </span></dt><dd> |
| delete the branch <code class="literal"><branch></code> irrespective of its merged status. |
| </dd><dt><span class="term"> |
| <code class="literal">git checkout <branch></code> |
| </span></dt><dd> |
| make the current branch <code class="literal"><branch></code>, updating the working |
| directory to reflect the version referenced by <code class="literal"><branch></code>. |
| </dd><dt><span class="term"> |
| <code class="literal">git checkout -b <new> <start-point></code> |
| </span></dt><dd> |
| create a new branch <code class="literal"><new></code> referencing <code class="literal"><start-point></code>, and |
| check it out. |
| </dd></dl></div><p>The special symbol "HEAD" can always be used to refer to the current |
| branch. In fact, Git uses a file named <code class="literal">HEAD</code> in the <code class="literal">.git</code> directory |
| to remember which branch is current:</p><pre class="literallayout">$ cat .git/HEAD |
| ref: refs/heads/master</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="detached-head"></a>Examining an old version without creating a new branch</h2></div></div></div><p>The <code class="literal">git checkout</code> command normally expects a branch head, but will also |
| accept an arbitrary commit; for example, you can check out the commit |
| referenced by a tag:</p><pre class="literallayout">$ git checkout v2.6.17 |
| Note: checking out 'v2.6.17'. |
| |
| You are in 'detached HEAD' state. You can look around, make experimental |
| changes and commit them, and you can discard any commits you make in this |
| state without impacting any branches by performing another checkout. |
| |
| If you want to create a new branch to retain commits you create, you may |
| do so (now or later) by using -b with the checkout command again. Example: |
| |
| git checkout -b new_branch_name |
| |
| HEAD is now at 427abfa Linux v2.6.17</pre><p>The HEAD then refers to the SHA-1 of the commit instead of to a branch, |
| and git branch shows that you are no longer on a branch:</p><pre class="literallayout">$ cat .git/HEAD |
| 427abfa28afedffadfca9dd8b067eb6d36bac53f |
| $ git branch |
| * (detached from v2.6.17) |
| master</pre><p>In this case we say that the HEAD is "detached".</p><p>This is an easy way to check out a particular version without having to |
| make up a name for the new branch. You can still create a new branch |
| (or tag) for this version later if you decide to.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="examining-remote-branches"></a>Examining branches from a remote repository</h2></div></div></div><p>The "master" branch that was created at the time you cloned is a copy |
| of the HEAD in the repository that you cloned from. That repository |
| may also have had other branches, though, and your local repository |
| keeps branches which track each of those remote branches, called |
| remote-tracking branches, which you |
| can view using the <code class="literal">-r</code> option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>:</p><pre class="literallayout">$ git branch -r |
| origin/HEAD |
| origin/html |
| origin/maint |
| origin/man |
| origin/master |
| origin/next |
| origin/pu |
| origin/todo</pre><p>In this example, "origin" is called a remote repository, or "remote" |
| for short. The branches of this repository are called "remote |
| branches" from our point of view. The remote-tracking branches listed |
| above were created based on the remote branches at clone time and will |
| be updated by <code class="literal">git fetch</code> (hence <code class="literal">git pull</code>) and <code class="literal">git push</code>. See |
| <a class="xref" href="#Updating-a-repository-With-git-fetch" title="Updating a repository with git fetch">the section called “Updating a repository with git fetch”</a> for details.</p><p>You might want to build on one of these remote-tracking branches |
| on a branch of your own, just as you would for a tag:</p><pre class="literallayout">$ git checkout -b my-todo-copy origin/todo</pre><p>You can also check out <code class="literal">origin/todo</code> directly to examine it or |
| write a one-off patch. See <a class="link" href="#detached-head" title="Examining an old version without creating a new branch">detached head</a>.</p><p>Note that the name "origin" is just the name that Git uses by default |
| to refer to the repository that you cloned from.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-git-stores-references"></a>Naming branches, tags, and other references</h2></div></div></div><p>Branches, remote-tracking branches, and tags are all references to |
| commits. All references are named with a slash-separated path name |
| starting with <code class="literal">refs</code>; the names we’ve been using so far are actually |
| shorthand:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| The branch <code class="literal">test</code> is short for <code class="literal">refs/heads/test</code>. |
| </li><li class="listitem"> |
| The tag <code class="literal">v2.6.18</code> is short for <code class="literal">refs/tags/v2.6.18</code>. |
| </li><li class="listitem"> |
| <code class="literal">origin/master</code> is short for <code class="literal">refs/remotes/origin/master</code>. |
| </li></ul></div><p>The full name is occasionally useful if, for example, there ever |
| exists a tag and a branch with the same name.</p><p>(Newly created refs are actually stored in the <code class="literal">.git/refs</code> directory, |
| under the path given by their name. However, for efficiency reasons |
| they may also be packed together in a single file; see |
| <a class="ulink" href="git-pack-refs.html" target="_top">git-pack-refs(1)</a>).</p><p>As another useful shortcut, the "HEAD" of a repository can be referred |
| to just using the name of that repository. So, for example, "origin" |
| is usually a shortcut for the HEAD branch in the repository "origin".</p><p>For the complete list of paths which Git checks for references, and |
| the order it uses to decide which to choose when there are multiple |
| references with the same shorthand name, see the "SPECIFYING |
| REVISIONS" section of <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a>.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="Updating-a-repository-With-git-fetch"></a>Updating a repository with git fetch</h2></div></div></div><p>After you clone a repository and commit a few changes of your own, you |
| may wish to check the original repository for updates.</p><p>The <code class="literal">git-fetch</code> command, with no arguments, will update all of the |
| remote-tracking branches to the latest version found in the original |
| repository. It will not touch any of your own branches—not even the |
| "master" branch that was created for you on clone.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetching-branches"></a>Fetching branches from other repositories</h2></div></div></div><p>You can also track branches from repositories other than the one you |
| cloned from, using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>:</p><pre class="literallayout">$ git remote add staging git://git.kernel.org/.../gregkh/staging.git |
| $ git fetch staging |
| ... |
| From git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging |
| * [new branch] master -> staging/master |
| * [new branch] staging-linus -> staging/staging-linus |
| * [new branch] staging-next -> staging/staging-next</pre><p>New remote-tracking branches will be stored under the shorthand name |
| that you gave <code class="literal">git remote add</code>, in this case <code class="literal">staging</code>:</p><pre class="literallayout">$ git branch -r |
| origin/HEAD -> origin/master |
| origin/master |
| staging/master |
| staging/staging-linus |
| staging/staging-next</pre><p>If you run <code class="literal">git fetch <remote></code> later, the remote-tracking branches |
| for the named <code class="literal"><remote></code> will be updated.</p><p>If you examine the file <code class="literal">.git/config</code>, you will see that Git has added |
| a new stanza:</p><pre class="literallayout">$ cat .git/config |
| ... |
| [remote "staging"] |
| url = git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git |
| fetch = +refs/heads/*:refs/remotes/staging/* |
| ...</pre><p>This is what causes Git to track the remote’s branches; you may modify |
| or delete these configuration options by editing <code class="literal">.git/config</code> with a |
| text editor. (See the "CONFIGURATION FILE" section of |
| <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for details.)</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="exploring-git-history"></a>Chapter 2. Exploring Git history</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-commits-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></div><p>Git is best thought of as a tool for storing the history of a |
| collection of files. It does this by storing compressed snapshots of |
| the contents of a file hierarchy, together with "commits" which show |
| the relationships between these snapshots.</p><p>Git provides extremely flexible and fast tools for exploring the |
| history of a project.</p><p>We start with one specialized tool that is useful for finding the |
| commit that introduced a bug into a project.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-bisect"></a>How to use bisect to find a regression</h2></div></div></div><p>Suppose version 2.6.18 of your project worked, but the version at |
| "master" crashes. Sometimes the best way to find the cause of such a |
| regression is to perform a brute-force search through the project’s |
| history to find the particular commit that caused the problem. The |
| <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command can help you do this:</p><pre class="literallayout">$ git bisect start |
| $ git bisect good v2.6.18 |
| $ git bisect bad master |
| Bisecting: 3537 revisions left to test after this |
| [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]</pre><p>If you run <code class="literal">git branch</code> at this point, you’ll see that Git has |
| temporarily moved you in "(no branch)". HEAD is now detached from any |
| branch and points directly to a commit (with commit id 65934) that |
| is reachable from "master" but not from v2.6.18. Compile and test it, |
| and see whether it crashes. Assume it does crash. Then:</p><pre class="literallayout">$ git bisect bad |
| Bisecting: 1769 revisions left to test after this |
| [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings</pre><p>checks out an older version. Continue like this, telling Git at each |
| stage whether the version it gives you is good or bad, and notice |
| that the number of revisions left to test is cut approximately in |
| half each time.</p><p>After about 13 tests (in this case), it will output the commit id of |
| the guilty commit. You can then examine the commit with |
| <a class="ulink" href="git-show.html" target="_top">git-show(1)</a>, find out who wrote it, and mail them your bug |
| report with the commit id. Finally, run</p><pre class="literallayout">$ git bisect reset</pre><p>to return you to the branch you were on before.</p><p>Note that the version which <code class="literal">git bisect</code> checks out for you at each |
| point is just a suggestion, and you’re free to try a different |
| version if you think it would be a good idea. For example, |
| occasionally you may land on a commit that broke something unrelated; |
| run</p><pre class="literallayout">$ git bisect visualize</pre><p>which will run gitk and label the commit it chose with a marker that |
| says "bisect". Choose a safe-looking commit nearby, note its commit |
| id, and check it out with:</p><pre class="literallayout">$ git reset --hard fb47ddb2db</pre><p>then test, run <code class="literal">bisect good</code> or <code class="literal">bisect bad</code> as appropriate, and |
| continue.</p><p>Instead of <code class="literal">git bisect visualize</code> and then <code class="literal">git reset --hard |
| fb47ddb2db</code>, you might just want to tell Git that you want to skip |
| the current commit:</p><pre class="literallayout">$ git bisect skip</pre><p>In this case, though, Git may not eventually be able to tell the first |
| bad one between some first skipped commits and a later bad commit.</p><p>There are also ways to automate the bisecting process if you have a |
| test script that can tell a good from a bad commit. See |
| <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> for more information about this and other <code class="literal">git |
| bisect</code> features.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="naming-commits"></a>Naming commits</h2></div></div></div><p>We have seen several ways of naming commits already:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| 40-hexdigit object name |
| </li><li class="listitem"> |
| branch name: refers to the commit at the head of the given |
| branch |
| </li><li class="listitem"> |
| tag name: refers to the commit pointed to by the given tag |
| (we’ve seen branches and tags are special cases of |
| <a class="link" href="#how-git-stores-references" title="Naming branches, tags, and other references">references</a>). |
| </li><li class="listitem"> |
| HEAD: refers to the head of the current branch |
| </li></ul></div><p>There are many more; see the "SPECIFYING REVISIONS" section of the |
| <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> man page for the complete list of ways to |
| name revisions. Some examples:</p><pre class="literallayout">$ git show fb47ddb2 # the first few characters of the object name |
| # are usually enough to specify it uniquely |
| $ git show HEAD^ # the parent of the HEAD commit |
| $ git show HEAD^^ # the grandparent |
| $ git show HEAD~4 # the great-great-grandparent</pre><p>Recall that merge commits may have more than one parent; by default, |
| <code class="literal">^</code> and <code class="literal">~</code> follow the first parent listed in the commit, but you can |
| also choose:</p><pre class="literallayout">$ git show HEAD^1 # show the first parent of HEAD |
| $ git show HEAD^2 # show the second parent of HEAD</pre><p>In addition to HEAD, there are several other special names for |
| commits:</p><p>Merges (to be discussed later), as well as operations such as |
| <code class="literal">git reset</code>, which change the currently checked-out commit, generally |
| set ORIG_HEAD to the value HEAD had before the current operation.</p><p>The <code class="literal">git fetch</code> operation always stores the head of the last fetched |
| branch in FETCH_HEAD. For example, if you run <code class="literal">git fetch</code> without |
| specifying a local branch as the target of the operation</p><pre class="literallayout">$ git fetch git://example.com/proj.git theirbranch</pre><p>the fetched commits will still be available from FETCH_HEAD.</p><p>When we discuss merges we’ll also see the special name MERGE_HEAD, |
| which refers to the other branch that we’re merging in to the current |
| branch.</p><p>The <a class="ulink" href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> command is a low-level command that is |
| occasionally useful for translating some name for a commit to the object |
| name for that commit:</p><pre class="literallayout">$ git rev-parse origin |
| e05db0fd4f31dde7005f075a84f96b360d05984b</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-tags"></a>Creating tags</h2></div></div></div><p>We can also create a tag to refer to a particular commit; after |
| running</p><pre class="literallayout">$ git tag stable-1 1b2e1d63ff</pre><p>You can use <code class="literal">stable-1</code> to refer to the commit 1b2e1d63ff.</p><p>This creates a "lightweight" tag. If you would also like to include a |
| comment with the tag, and possibly sign it cryptographically, then you |
| should create a tag object instead; see the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> man page |
| for details.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="browsing-revisions"></a>Browsing revisions</h2></div></div></div><p>The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> command can show lists of commits. On its |
| own, it shows all commits reachable from the parent commit; but you |
| can also make more specific requests:</p><pre class="literallayout">$ git log v2.5.. # commits since (not reachable from) v2.5 |
| $ git log test..master # commits reachable from master but not test |
| $ git log master..test # ...reachable from test but not master |
| $ git log master...test # ...reachable from either test or master, |
| # but not both |
| $ git log --since="2 weeks ago" # commits from the last 2 weeks |
| $ git log Makefile # commits which modify Makefile |
| $ git log fs/ # ... which modify any file under fs/ |
| $ git log -S'foo()' # commits which add or remove any file data |
| # matching the string 'foo()'</pre><p>And of course you can combine all of these; the following finds |
| commits since v2.5 which touch the <code class="literal">Makefile</code> or any file under <code class="literal">fs</code>:</p><pre class="literallayout">$ git log v2.5.. Makefile fs/</pre><p>You can also ask git log to show patches:</p><pre class="literallayout">$ git log -p</pre><p>See the <code class="literal">--pretty</code> option in the <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> man page for more |
| display options.</p><p>Note that git log starts with the most recent commit and works |
| backwards through the parents; however, since Git history can contain |
| multiple independent lines of development, the particular order that |
| commits are listed in may be somewhat arbitrary.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="generating-diffs"></a>Generating diffs</h2></div></div></div><p>You can generate diffs between any two versions using |
| <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>:</p><pre class="literallayout">$ git diff master..test</pre><p>That will produce the diff between the tips of the two branches. If |
| you’d prefer to find the diff from their common ancestor to test, you |
| can use three dots instead of two:</p><pre class="literallayout">$ git diff master...test</pre><p>Sometimes what you want instead is a set of patches; for this you can |
| use <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a>:</p><pre class="literallayout">$ git format-patch master..test</pre><p>will generate a file with a patch for each commit reachable from test |
| but not from master.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="viewing-old-file-versions"></a>Viewing old file versions</h2></div></div></div><p>You can always view an old version of a file by just checking out the |
| correct revision first. But sometimes it is more convenient to be |
| able to view an old version of a single file without checking |
| anything out; this command does that:</p><pre class="literallayout">$ git show v2.5:fs/locks.c</pre><p>Before the colon may be anything that names a commit, and after it |
| may be any path to a file tracked by Git.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="history-examples"></a>Examples</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="counting-commits-on-a-branch"></a>Counting the number of commits on a branch</h3></div></div></div><p>Suppose you want to know how many commits you’ve made on <code class="literal">mybranch</code> |
| since it diverged from <code class="literal">origin</code>:</p><pre class="literallayout">$ git log --pretty=oneline origin..mybranch | wc -l</pre><p>Alternatively, you may often see this sort of thing done with the |
| lower-level command <a class="ulink" href="git-rev-list.html" target="_top">git-rev-list(1)</a>, which just lists the SHA-1’s |
| of all the given commits:</p><pre class="literallayout">$ git rev-list origin..mybranch | wc -l</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="checking-for-equal-branches"></a>Check whether two branches point at the same history</h3></div></div></div><p>Suppose you want to check whether two branches point at the same point |
| in history.</p><pre class="literallayout">$ git diff origin..master</pre><p>will tell you whether the contents of the project are the same at the |
| two branches; in theory, however, it’s possible that the same project |
| contents could have been arrived at by two different historical |
| routes. You could compare the object names:</p><pre class="literallayout">$ git rev-list origin |
| e05db0fd4f31dde7005f075a84f96b360d05984b |
| $ git rev-list master |
| e05db0fd4f31dde7005f075a84f96b360d05984b</pre><p>Or you could recall that the <code class="literal">...</code> operator selects all commits |
| reachable from either one reference or the other but not |
| both; so</p><pre class="literallayout">$ git log origin...master</pre><p>will return no commits when the two branches are equal.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="finding-tagged-descendants"></a>Find first tagged version including a given fix</h3></div></div></div><p>Suppose you know that the commit e05db0fd fixed a certain problem. |
| You’d like to find the earliest tagged release that contains that |
| fix.</p><p>Of course, there may be more than one answer—if the history branched |
| after commit e05db0fd, then there could be multiple "earliest" tagged |
| releases.</p><p>You could just visually inspect the commits since e05db0fd:</p><pre class="literallayout">$ gitk e05db0fd..</pre><p>or you can use <a class="ulink" href="git-name-rev.html" target="_top">git-name-rev(1)</a>, which will give the commit a |
| name based on any tag it finds pointing to one of the commit’s |
| descendants:</p><pre class="literallayout">$ git name-rev --tags e05db0fd |
| e05db0fd tags/v1.5.0-rc1^0~23</pre><p>The <a class="ulink" href="git-describe.html" target="_top">git-describe(1)</a> command does the opposite, naming the |
| revision using a tag on which the given commit is based:</p><pre class="literallayout">$ git describe e05db0fd |
| v1.5.0-rc0-260-ge05db0f</pre><p>but that may sometimes help you guess which tags might come after the |
| given commit.</p><p>If you just want to verify whether a given tagged version contains a |
| given commit, you could use <a class="ulink" href="git-merge-base.html" target="_top">git-merge-base(1)</a>:</p><pre class="literallayout">$ git merge-base e05db0fd v1.5.0-rc1 |
| e05db0fd4f31dde7005f075a84f96b360d05984b</pre><p>The merge-base command finds a common ancestor of the given commits, |
| and always returns one or the other in the case where one is a |
| descendant of the other; so the above output shows that e05db0fd |
| actually is an ancestor of v1.5.0-rc1.</p><p>Alternatively, note that</p><pre class="literallayout">$ git log v1.5.0-rc1..e05db0fd</pre><p>will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, |
| because it outputs only commits that are not reachable from v1.5.0-rc1.</p><p>As yet another alternative, the <a class="ulink" href="git-show-branch.html" target="_top">git-show-branch(1)</a> command lists |
| the commits reachable from its arguments with a display on the left-hand |
| side that indicates which arguments that commit is reachable from. |
| So, if you run something like</p><pre class="literallayout">$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2 |
| ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if |
| available |
| ! [v1.5.0-rc0] GIT v1.5.0 preview |
| ! [v1.5.0-rc1] GIT v1.5.0-rc1 |
| ! [v1.5.0-rc2] GIT v1.5.0-rc2 |
| ...</pre><p>then a line like</p><pre class="literallayout">+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if |
| available</pre><p>shows that e05db0fd is reachable from itself, from v1.5.0-rc1, |
| and from v1.5.0-rc2, and not from v1.5.0-rc0.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="showing-commits-unique-to-a-branch"></a>Showing commits unique to a given branch</h3></div></div></div><p>Suppose you would like to see all the commits reachable from the branch |
| head named <code class="literal">master</code> but not from any other head in your repository.</p><p>We can list all the heads in this repository with |
| <a class="ulink" href="git-show-ref.html" target="_top">git-show-ref(1)</a>:</p><pre class="literallayout">$ git show-ref --heads |
| bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial |
| db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint |
| a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master |
| 24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2 |
| 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes</pre><p>We can get just the branch-head names, and remove <code class="literal">master</code>, with |
| the help of the standard utilities cut and grep:</p><pre class="literallayout">$ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master' |
| refs/heads/core-tutorial |
| refs/heads/maint |
| refs/heads/tutorial-2 |
| refs/heads/tutorial-fixes</pre><p>And then we can ask to see all the commits reachable from master |
| but not from these other heads:</p><pre class="literallayout">$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 | |
| grep -v '^refs/heads/master' )</pre><p>Obviously, endless variations are possible; for example, to see all |
| commits reachable from some head but not from any tag in the repository:</p><pre class="literallayout">$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )</pre><p>(See <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> for explanations of commit-selecting |
| syntax such as <code class="literal">--not</code>.)</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="making-a-release"></a>Creating a changelog and tarball for a software release</h3></div></div></div><p>The <a class="ulink" href="git-archive.html" target="_top">git-archive(1)</a> command can create a tar or zip archive from |
| any version of a project; for example:</p><pre class="literallayout">$ git archive -o latest.tar.gz --prefix=project/ HEAD</pre><p>will use HEAD to produce a gzipped tar archive in which each filename |
| is preceded by <code class="literal">project/</code>. The output file format is inferred from |
| the output file extension if possible, see <a class="ulink" href="git-archive.html" target="_top">git-archive(1)</a> for |
| details.</p><p>Versions of Git older than 1.7.7 don’t know about the <code class="literal">tar.gz</code> format, |
| you’ll need to use gzip explicitly:</p><pre class="literallayout">$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz</pre><p>If you’re releasing a new version of a software project, you may want |
| to simultaneously make a changelog to include in the release |
| announcement.</p><p>Linus Torvalds, for example, makes new kernel releases by tagging them, |
| then running:</p><pre class="literallayout">$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7</pre><p>where release-script is a shell script that looks like:</p><pre class="literallayout">#!/bin/sh |
| stable="$1" |
| last="$2" |
| new="$3" |
| echo "# git tag v$new" |
| echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz" |
| echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz" |
| echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new" |
| echo "git shortlog --no-merges v$new ^v$last > ../ShortLog" |
| echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"</pre><p>and then he just cut-and-pastes the output commands after verifying that |
| they look OK.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="Finding-commits-With-given-Content"></a>Finding commits referencing a file with given content</h3></div></div></div><p>Somebody hands you a copy of a file, and asks which commits modified a |
| file such that it contained the given content either before or after the |
| commit. You can find out with this:</p><pre class="literallayout">$ git log --raw --abbrev=40 --pretty=oneline | |
| grep -B 1 `git hash-object filename`</pre><p>Figuring out why this works is left as an exercise to the (advanced) |
| student. The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a>, <a class="ulink" href="git-diff-tree.html" target="_top">git-diff-tree(1)</a>, and |
| <a class="ulink" href="git-hash-object.html" target="_top">git-hash-object(1)</a> man pages may prove helpful.</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="Developing-With-git"></a>Chapter 3. Developing with Git</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#telling-git-your-name">Telling Git your name</a></span></dt><dt><span class="section"><a href="#creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">How to make a commit</a></span></dt><dt><span class="section"><a href="#creating-good-commit-messages">Creating good commit messages</a></span></dt><dt><span class="section"><a href="#ignoring-files">Ignoring files</a></span></dt><dt><span class="section"><a href="#how-to-merge">How to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dd><dl><dt><span class="section"><a href="#conflict-resolution">Getting conflict-resolution help during a merge</a></span></dt></dl></dd><dt><span class="section"><a href="#undoing-a-merge">Undoing a merge</a></span></dt><dt><span class="section"><a href="#fast-forwards">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#fixing-mistakes">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#reverting-a-commit">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#fixing-a-mistake-by-rewriting-history">Fixing a mistake by rewriting history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</a></span></dt><dt><span class="section"><a href="#interrupted-work">Temporarily setting aside work in progress</a></span></dt></dl></dd><dt><span class="section"><a href="#ensuring-good-performance">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#ensuring-reliability">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#checking-for-corruption">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#recovering-lost-changes">Recovering lost changes</a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="telling-git-your-name"></a>Telling Git your name</h2></div></div></div><p>Before creating any commits, you should introduce yourself to Git. |
| The easiest way to do so is to use <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>:</p><pre class="literallayout">$ git config --global user.name 'Your Name Comes Here' |
| $ git config --global user.email 'you@yourdomain.example.com'</pre><p>Which will add the following to a file named <code class="literal">.gitconfig</code> in your |
| home directory:</p><pre class="literallayout">[user] |
| name = Your Name Comes Here |
| email = you@yourdomain.example.com</pre><p>See the "CONFIGURATION FILE" section of <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for |
| details on the configuration file. The file is plain text, so you can |
| also edit it with your favorite editor.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-a-new-repository"></a>Creating a new repository</h2></div></div></div><p>Creating a new repository from scratch is very easy:</p><pre class="literallayout">$ mkdir project |
| $ cd project |
| $ git init</pre><p>If you have some initial content (say, a tarball):</p><pre class="literallayout">$ tar xzvf project.tar.gz |
| $ cd project |
| $ git init |
| $ git add . # include everything below ./ in the first commit: |
| $ git commit</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-make-a-commit"></a>How to make a commit</h2></div></div></div><p>Creating a new commit takes three steps:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> |
| Making some changes to the working directory using your |
| favorite editor. |
| </li><li class="listitem"> |
| Telling Git about your changes. |
| </li><li class="listitem"> |
| Creating the commit using the content you told Git about |
| in step 2. |
| </li></ol></div><p>In practice, you can interleave and repeat steps 1 and 2 as many |
| times as you want: in order to keep track of what you want committed |
| at step 3, Git maintains a snapshot of the tree’s contents in a |
| special staging area called "the index."</p><p>At the beginning, the content of the index will be identical to |
| that of the HEAD. The command <code class="literal">git diff --cached</code>, which shows |
| the difference between the HEAD and the index, should therefore |
| produce no output at that point.</p><p>Modifying the index is easy:</p><p>To update the index with the contents of a new or modified file, use</p><pre class="literallayout">$ git add path/to/file</pre><p>To remove a file from the index and from the working tree, use</p><pre class="literallayout">$ git rm path/to/file</pre><p>After each step you can verify that</p><pre class="literallayout">$ git diff --cached</pre><p>always shows the difference between the HEAD and the index file—this |
| is what you’d commit if you created the commit now—and that</p><pre class="literallayout">$ git diff</pre><p>shows the difference between the working tree and the index file.</p><p>Note that <code class="literal">git add</code> always adds just the current contents of a file |
| to the index; further changes to the same file will be ignored unless |
| you run <code class="literal">git add</code> on the file again.</p><p>When you’re ready, just run</p><pre class="literallayout">$ git commit</pre><p>and Git will prompt you for a commit message and then create the new |
| commit. Check to make sure it looks like what you expected with</p><pre class="literallayout">$ git show</pre><p>As a special shortcut,</p><pre class="literallayout">$ git commit -a</pre><p>will update the index with any files that you’ve modified or removed |
| and create a commit, all in one step.</p><p>A number of commands are useful for keeping track of what you’re |
| about to commit:</p><pre class="literallayout">$ git diff --cached # difference between HEAD and the index; what |
| # would be committed if you ran "commit" now. |
| $ git diff # difference between the index file and your |
| # working directory; changes that would not |
| # be included if you ran "commit" now. |
| $ git diff HEAD # difference between HEAD and working tree; what |
| # would be committed if you ran "commit -a" now. |
| $ git status # a brief per-file summary of the above.</pre><p>You can also use <a class="ulink" href="git-gui.html" target="_top">git-gui(1)</a> to create commits, view changes in |
| the index and the working tree files, and individually select diff hunks |
| for inclusion in the index (by right-clicking on the diff hunk and |
| choosing "Stage Hunk For Commit").</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-good-commit-messages"></a>Creating good commit messages</h2></div></div></div><p>Though not required, it’s a good idea to begin the commit message |
| with a single short (less than 50 character) line summarizing the |
| change, followed by a blank line and then a more thorough |
| description. The text up to the first blank line in a commit |
| message is treated as the commit title, and that title is used |
| throughout Git. For example, <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a> turns a |
| commit into email, and it uses the title on the Subject line and the |
| rest of the commit in the body.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ignoring-files"></a>Ignoring files</h2></div></div></div><p>A project will often generate files that you do <span class="emphasis"><em>not</em></span> want to track with Git. |
| This typically includes files generated by a build process or temporary |
| backup files made by your editor. Of course, <span class="emphasis"><em>not</em></span> tracking files with Git |
| is just a matter of <span class="emphasis"><em>not</em></span> calling <code class="literal">git add</code> on them. But it quickly becomes |
| annoying to have these untracked files lying around; e.g. they make |
| <code class="literal">git add .</code> practically useless, and they keep showing up in the output of |
| <code class="literal">git status</code>.</p><p>You can tell Git to ignore certain files by creating a file called |
| <code class="literal">.gitignore</code> in the top level of your working directory, with contents |
| such as:</p><pre class="literallayout"># Lines starting with '#' are considered comments. |
| # Ignore any file named foo.txt. |
| foo.txt |
| # Ignore (generated) html files, |
| *.html |
| # except foo.html which is maintained by hand. |
| !foo.html |
| # Ignore objects and archives. |
| *.[oa]</pre><p>See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for a detailed explanation of the syntax. You can |
| also place .gitignore files in other directories in your working tree, and they |
| will apply to those directories and their subdirectories. The <code class="literal">.gitignore</code> |
| files can be added to your repository like any other files (just run <code class="literal">git add |
| .gitignore</code> and <code class="literal">git commit</code>, as usual), which is convenient when the exclude |
| patterns (such as patterns matching build output files) would also make sense |
| for other users who clone your repository.</p><p>If you wish the exclude patterns to affect only certain repositories |
| (instead of every repository for a given project), you may instead put |
| them in a file in your repository named <code class="literal">.git/info/exclude</code>, or in any |
| file specified by the <code class="literal">core.excludesFile</code> configuration variable. |
| Some Git commands can also take exclude patterns directly on the |
| command line. See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for the details.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-merge"></a>How to merge</h2></div></div></div><p>You can rejoin two diverging branches of development using |
| <a class="ulink" href="git-merge.html" target="_top">git-merge(1)</a>:</p><pre class="literallayout">$ git merge branchname</pre><p>merges the development in the branch <code class="literal">branchname</code> into the current |
| branch.</p><p>A merge is made by combining the changes made in <code class="literal">branchname</code> and the |
| changes made up to the latest commit in your current branch since |
| their histories forked. The work tree is overwritten by the result of |
| the merge when this combining is done cleanly, or overwritten by a |
| half-merged results when this combining results in conflicts. |
| Therefore, if you have uncommitted changes touching the same files as |
| the ones impacted by the merge, Git will refuse to proceed. Most of |
| the time, you will want to commit your changes before you can merge, |
| and if you don’t, then <a class="ulink" href="git-stash.html" target="_top">git-stash(1)</a> can take these changes |
| away while you’re doing the merge, and reapply them afterwards.</p><p>If the changes are independent enough, Git will automatically complete |
| the merge and commit the result (or reuse an existing commit in case |
| of <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>, see below). On the other hand, |
| if there are conflicts—for example, if the same file is |
| modified in two different ways in the remote branch and the local |
| branch—then you are warned; the output may look something like this:</p><pre class="literallayout">$ git merge next |
| 100% (4/4) done |
| Auto-merged file.txt |
| CONFLICT (content): Merge conflict in file.txt |
| Automatic merge failed; fix conflicts and then commit the result.</pre><p>Conflict markers are left in the problematic files, and after |
| you resolve the conflicts manually, you can update the index |
| with the contents and run Git commit, as you normally would when |
| creating a new file.</p><p>If you examine the resulting commit using gitk, you will see that it |
| has two parents, one pointing to the top of the current branch, and |
| one to the top of the other branch.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="resolving-a-merge"></a>Resolving a merge</h2></div></div></div><p>When a merge isn’t resolved automatically, Git leaves the index and |
| the working tree in a special state that gives you all the |
| information you need to help resolve the merge.</p><p>Files with conflicts are marked specially in the index, so until you |
| resolve the problem and update the index, <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> will |
| fail:</p><pre class="literallayout">$ git commit |
| file.txt: needs merge</pre><p>Also, <a class="ulink" href="git-status.html" target="_top">git-status(1)</a> will list those files as "unmerged", and the |
| files with conflicts will have conflict markers added, like this:</p><pre class="literallayout"><<<<<<< HEAD:file.txt |
| Hello world |
| ======= |
| Goodbye |
| >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</pre><p>All you need to do is edit the files to resolve the conflicts, and then</p><pre class="literallayout">$ git add file.txt |
| $ git commit</pre><p>Note that the commit message will already be filled in for you with |
| some information about the merge. Normally you can just use this |
| default message unchanged, but you may add additional commentary of |
| your own if desired.</p><p>The above is all you need to know to resolve a simple merge. But Git |
| also provides more information to help resolve conflicts:</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="conflict-resolution"></a>Getting conflict-resolution help during a merge</h3></div></div></div><p>All of the changes that Git was able to merge automatically are |
| already added to the index file, so <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> shows only |
| the conflicts. It uses an unusual syntax:</p><pre class="literallayout">$ git diff |
| diff --cc file.txt |
| index 802992c,2b60207..0000000 |
| --- a/file.txt |
| +++ b/file.txt |
| @@@ -1,1 -1,1 +1,5 @@@ |
| ++<<<<<<< HEAD:file.txt |
| +Hello world |
| ++======= |
| + Goodbye |
| ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</pre><p>Recall that the commit which will be committed after we resolve this |
| conflict will have two parents instead of the usual one: one parent |
| will be HEAD, the tip of the current branch; the other will be the |
| tip of the other branch, which is stored temporarily in MERGE_HEAD.</p><p>During the merge, the index holds three versions of each file. Each of |
| these three "file stages" represents a different version of the file:</p><pre class="literallayout">$ git show :1:file.txt # the file in a common ancestor of both branches |
| $ git show :2:file.txt # the version from HEAD. |
| $ git show :3:file.txt # the version from MERGE_HEAD.</pre><p>When you ask <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> to show the conflicts, it runs a |
| three-way diff between the conflicted merge results in the work tree with |
| stages 2 and 3 to show only hunks whose contents come from both sides, |
| mixed (in other words, when a hunk’s merge results come only from stage 2, |
| that part is not conflicting and is not shown. Same for stage 3).</p><p>The diff above shows the differences between the working-tree version of |
| file.txt and the stage 2 and stage 3 versions. So instead of preceding |
| each line by a single <code class="literal">+</code> or <code class="literal">-</code>, it now uses two columns: the first |
| column is used for differences between the first parent and the working |
| directory copy, and the second for differences between the second parent |
| and the working directory copy. (See the "COMBINED DIFF FORMAT" section |
| of <a class="ulink" href="git-diff-files.html" target="_top">git-diff-files(1)</a> for a details of the format.)</p><p>After resolving the conflict in the obvious way (but before updating the |
| index), the diff will look like:</p><pre class="literallayout">$ git diff |
| diff --cc file.txt |
| index 802992c,2b60207..0000000 |
| --- a/file.txt |
| +++ b/file.txt |
| @@@ -1,1 -1,1 +1,1 @@@ |
| - Hello world |
| -Goodbye |
| ++Goodbye world</pre><p>This shows that our resolved version deleted "Hello world" from the |
| first parent, deleted "Goodbye" from the second parent, and added |
| "Goodbye world", which was previously absent from both.</p><p>Some special diff options allow diffing the working directory against |
| any of these stages:</p><pre class="literallayout">$ git diff -1 file.txt # diff against stage 1 |
| $ git diff --base file.txt # same as the above |
| $ git diff -2 file.txt # diff against stage 2 |
| $ git diff --ours file.txt # same as the above |
| $ git diff -3 file.txt # diff against stage 3 |
| $ git diff --theirs file.txt # same as the above.</pre><p>The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> and <a class="ulink" href="gitk.html" target="_top">gitk(1)</a> commands also provide special help |
| for merges:</p><pre class="literallayout">$ git log --merge |
| $ gitk --merge</pre><p>These will display all commits which exist only on HEAD or on |
| MERGE_HEAD, and which touch an unmerged file.</p><p>You may also use <a class="ulink" href="git-mergetool.html" target="_top">git-mergetool(1)</a>, which lets you merge the |
| unmerged files using external tools such as Emacs or kdiff3.</p><p>Each time you resolve the conflicts in a file and update the index:</p><pre class="literallayout">$ git add file.txt</pre><p>the different stages of that file will be "collapsed", after which |
| <code class="literal">git diff</code> will (by default) no longer show diffs for that file.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="undoing-a-merge"></a>Undoing a merge</h2></div></div></div><p>If you get stuck and decide to just give up and throw the whole mess |
| away, you can always return to the pre-merge state with</p><pre class="literallayout">$ git reset --hard HEAD</pre><p>Or, if you’ve already committed the merge that you want to throw away,</p><pre class="literallayout">$ git reset --hard ORIG_HEAD</pre><p>However, this last command can be dangerous in some cases—never |
| throw away a commit you have already committed if that commit may |
| itself have been merged into another branch, as doing so may confuse |
| further merges.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fast-forwards"></a>Fast-forward merges</h2></div></div></div><p>There is one special case not mentioned above, which is treated |
| differently. Normally, a merge results in a merge commit, with two |
| parents, one pointing at each of the two lines of development that |
| were merged.</p><p>However, if the current branch is an ancestor of the other—so every commit |
| present in the current branch is already contained in the other branch—then Git |
| just performs a "fast-forward"; the head of the current branch is moved forward |
| to point at the head of the merged-in branch, without any new commits being |
| created.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fixing-mistakes"></a>Fixing mistakes</h2></div></div></div><p>If you’ve messed up the working tree, but haven’t yet committed your |
| mistake, you can return the entire working tree to the last committed |
| state with</p><pre class="literallayout">$ git reset --hard HEAD</pre><p>If you make a commit that you later wish you hadn’t, there are two |
| fundamentally different ways to fix the problem:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> |
| You can create a new commit that undoes whatever was done |
| by the old commit. This is the correct thing if your |
| mistake has already been made public. |
| </li><li class="listitem"> |
| You can go back and modify the old commit. You should |
| never do this if you have already made the history public; |
| Git does not normally expect the "history" of a project to |
| change, and cannot correctly perform repeated merges from |
| a branch that has had its history changed. |
| </li></ol></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reverting-a-commit"></a>Fixing a mistake with a new commit</h3></div></div></div><p>Creating a new commit that reverts an earlier change is very easy; |
| just pass the <a class="ulink" href="git-revert.html" target="_top">git-revert(1)</a> command a reference to the bad |
| commit; for example, to revert the most recent commit:</p><pre class="literallayout">$ git revert HEAD</pre><p>This will create a new commit which undoes the change in HEAD. You |
| will be given a chance to edit the commit message for the new commit.</p><p>You can also revert an earlier change, for example, the next-to-last:</p><pre class="literallayout">$ git revert HEAD^</pre><p>In this case Git will attempt to undo the old change while leaving |
| intact any changes made since then. If more recent changes overlap |
| with the changes to be reverted, then you will be asked to fix |
| conflicts manually, just as in the case of <a class="link" href="#resolving-a-merge" title="Resolving a merge">resolving a merge</a>.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="fixing-a-mistake-by-rewriting-history"></a>Fixing a mistake by rewriting history</h3></div></div></div><p>If the problematic commit is the most recent commit, and you have not |
| yet made that commit public, then you may just |
| <a class="link" href="#undoing-a-merge" title="Undoing a merge">destroy it using <code class="literal">git reset</code></a>.</p><p>Alternatively, you |
| can edit the working directory and update the index to fix your |
| mistake, just as if you were going to <a class="link" href="#how-to-make-a-commit" title="How to make a commit">create a new commit</a>, then run</p><pre class="literallayout">$ git commit --amend</pre><p>which will replace the old commit by a new commit incorporating your |
| changes, giving you a chance to edit the old commit message first.</p><p>Again, you should never do this to a commit that may already have |
| been merged into another branch; use <a class="ulink" href="git-revert.html" target="_top">git-revert(1)</a> instead in |
| that case.</p><p>It is also possible to replace commits further back in the history, but |
| this is an advanced topic to be left for |
| <a class="link" href="#cleaning-up-history" title="Chapter 5. Rewriting history and maintaining patch series">another chapter</a>.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="checkout-of-path"></a>Checking out an old version of a file</h3></div></div></div><p>In the process of undoing a previous bad change, you may find it |
| useful to check out an older version of a particular file using |
| <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>. We’ve used <code class="literal">git checkout</code> before to switch |
| branches, but it has quite different behavior if it is given a path |
| name: the command</p><pre class="literallayout">$ git checkout HEAD^ path/to/file</pre><p>replaces path/to/file by the contents it had in the commit HEAD^, and |
| also updates the index to match. It does not change branches.</p><p>If you just want to look at an old version of the file, without |
| modifying the working directory, you can do that with |
| <a class="ulink" href="git-show.html" target="_top">git-show(1)</a>:</p><pre class="literallayout">$ git show HEAD^:path/to/file</pre><p>which will display the given version of the file.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="interrupted-work"></a>Temporarily setting aside work in progress</h3></div></div></div><p>While you are in the middle of working on something complicated, you |
| find an unrelated but obvious and trivial bug. You would like to fix it |
| before continuing. You can use <a class="ulink" href="git-stash.html" target="_top">git-stash(1)</a> to save the current |
| state of your work, and after fixing the bug (or, optionally after doing |
| so on a different branch and then coming back), unstash the |
| work-in-progress changes.</p><pre class="literallayout">$ git stash push -m "work in progress for foo feature"</pre><p>This command will save your changes away to the <code class="literal">stash</code>, and |
| reset your working tree and the index to match the tip of your |
| current branch. Then you can make your fix as usual.</p><pre class="literallayout">... edit and test ... |
| $ git commit -a -m "blorpl: typofix"</pre><p>After that, you can go back to what you were working on with |
| <code class="literal">git stash pop</code>:</p><pre class="literallayout">$ git stash pop</pre></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ensuring-good-performance"></a>Ensuring good performance</h2></div></div></div><p>On large repositories, Git depends on compression to keep the history |
| information from taking up too much space on disk or in memory. Some |
| Git commands may automatically run <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a>, so you don’t |
| have to worry about running it manually. However, compressing a large |
| repository may take a while, so you may want to call <code class="literal">gc</code> explicitly |
| to avoid automatic compression kicking in when it is not convenient.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ensuring-reliability"></a>Ensuring reliability</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="checking-for-corruption"></a>Checking the repository for corruption</h3></div></div></div><p>The <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a> command runs a number of self-consistency checks |
| on the repository, and reports on any problems. This may take some |
| time.</p><pre class="literallayout">$ git fsck |
| dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 |
| dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 |
| dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 |
| dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb |
| dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f |
| dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e |
| dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085 |
| dangling tree b24c2473f1fd3d91352a624795be026d64c8841f |
| ...</pre><p>You will see informational messages on dangling objects. They are objects |
| that still exist in the repository but are no longer referenced by any of |
| your branches, and can (and will) be removed after a while with <code class="literal">gc</code>. |
| You can run <code class="literal">git fsck --no-dangling</code> to suppress these messages, and still |
| view real errors.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="recovering-lost-changes"></a>Recovering lost changes</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="reflogs"></a>Reflogs</h4></div></div></div><p>Say you modify a branch with <a class="link" href="#fixing-mistakes" title="Fixing mistakes"><code class="literal">git reset --hard</code></a>, |
| and then realize that the branch was the only reference you had to |
| that point in history.</p><p>Fortunately, Git also keeps a log, called a "reflog", of all the |
| previous values of each branch. So in this case you can still find the |
| old history using, for example,</p><pre class="literallayout">$ git log master@{1}</pre><p>This lists the commits reachable from the previous version of the |
| <code class="literal">master</code> branch head. This syntax can be used with any Git command |
| that accepts a commit, not just with <code class="literal">git log</code>. Some other examples:</p><pre class="literallayout">$ git show master@{2} # See where the branch pointed 2, |
| $ git show master@{3} # 3, ... changes ago. |
| $ gitk master@{yesterday} # See where it pointed yesterday, |
| $ gitk master@{"1 week ago"} # ... or last week |
| $ git log --walk-reflogs master # show reflog entries for master</pre><p>A separate reflog is kept for the HEAD, so</p><pre class="literallayout">$ git show HEAD@{"1 week ago"}</pre><p>will show what HEAD pointed to one week ago, not what the current branch |
| pointed to one week ago. This allows you to see the history of what |
| you’ve checked out.</p><p>The reflogs are kept by default for 30 days, after which they may be |
| pruned. See <a class="ulink" href="git-reflog.html" target="_top">git-reflog(1)</a> and <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a> to learn |
| how to control this pruning, and see the "SPECIFYING REVISIONS" |
| section of <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> for details.</p><p>Note that the reflog history is very different from normal Git history. |
| While normal history is shared by every repository that works on the |
| same project, the reflog history is not shared: it tells you only about |
| how the branches in your local repository have changed over time.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="dangling-object-recovery"></a>Examining dangling objects</h4></div></div></div><p>In some situations the reflog may not be able to save you. For example, |
| suppose you delete a branch, then realize you need the history it |
| contained. The reflog is also deleted; however, if you have not yet |
| pruned the repository, then you may still be able to find the lost |
| commits in the dangling objects that <code class="literal">git fsck</code> reports. See |
| <a class="xref" href="#dangling-objects" title="Dangling objects">the section called “Dangling objects”</a> for the details.</p><pre class="literallayout">$ git fsck |
| dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 |
| dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 |
| dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 |
| ...</pre><p>You can examine |
| one of those dangling commits with, for example,</p><pre class="literallayout">$ gitk 7281251ddd --not --all</pre><p>which does what it sounds like: it says that you want to see the commit |
| history that is described by the dangling commit(s), but not the |
| history that is described by all your existing branches and tags. Thus |
| you get exactly the history reachable from that commit that is lost. |
| (And notice that it might not be just one commit: we only report the |
| "tip of the line" as being dangling, but there might be a whole deep |
| and complex commit history that was dropped.)</p><p>If you decide you want the history back, you can always create a new |
| reference pointing to it, for example, a new branch:</p><pre class="literallayout">$ git branch recovered-branch 7281251ddd</pre><p>Other types of dangling objects (blobs and trees) are also possible, and |
| dangling objects can arise in other situations.</p></div></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="sharing-development"></a>Chapter 4. Sharing development with others</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#getting-updates-With-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#submitting-patches">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#importing-patches">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#public-repositories">Public Git repositories</a></span></dt><dd><dl><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a Git repository via the Git protocol</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via HTTP</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#forcing-push">What to do when a push fails</a></span></dt><dt><span class="section"><a href="#setting-up-a-shared-repository">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#setting-up-gitweb">Allowing web browsing of a repository</a></span></dt></dl></dd><dt><span class="section"><a href="#how-to-get-a-git-repository-with-minimal-history">How to get a Git repository with minimal history</a></span></dt><dt><span class="section"><a href="#sharing-development-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#maintaining-topic-branches">Maintaining topic branches for a Linux subsystem maintainer</a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="getting-updates-With-git-pull"></a>Getting updates with git pull</h2></div></div></div><p>After you clone a repository and commit a few changes of your own, you |
| may wish to check the original repository for updates and merge them |
| into your own work.</p><p>We have already seen <a class="link" href="#Updating-a-repository-With-git-fetch" title="Updating a repository with git fetch">how to keep remote-tracking branches up to date</a> with <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>, |
| and how to merge two branches. So you can merge in changes from the |
| original repository’s master branch with:</p><pre class="literallayout">$ git fetch |
| $ git merge origin/master</pre><p>However, the <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a> command provides a way to do this in |
| one step:</p><pre class="literallayout">$ git pull origin master</pre><p>In fact, if you have <code class="literal">master</code> checked out, then this branch has been |
| configured by <code class="literal">git clone</code> to get changes from the HEAD branch of the |
| origin repository. So often you can |
| accomplish the above with just a simple</p><pre class="literallayout">$ git pull</pre><p>This command will fetch changes from the remote branches to your |
| remote-tracking branches <code class="literal">origin/*</code>, and merge the default branch into |
| the current branch.</p><p>More generally, a branch that is created from a remote-tracking branch |
| will pull |
| by default from that branch. See the descriptions of the |
| <code class="literal">branch.<name>.remote</code> and <code class="literal">branch.<name>.merge</code> options in |
| <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>, and the discussion of the <code class="literal">--track</code> option in |
| <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>, to learn how to control these defaults.</p><p>In addition to saving you keystrokes, <code class="literal">git pull</code> also helps you by |
| producing a default commit message documenting the branch and |
| repository that you pulled from.</p><p>(But note that no such commit will be created in the case of a |
| <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>; instead, your branch will just be |
| updated to point to the latest commit from the upstream branch.)</p><p>The <code class="literal">git pull</code> command can also be given <code class="literal">.</code> as the "remote" repository, |
| in which case it just merges in a branch from the current repository; so |
| the commands</p><pre class="literallayout">$ git pull . branch |
| $ git merge branch</pre><p>are roughly equivalent.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="submitting-patches"></a>Submitting patches to a project</h2></div></div></div><p>If you just have a few changes, the simplest way to submit them may |
| just be to send them as patches in email:</p><p>First, use <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a>; for example:</p><pre class="literallayout">$ git format-patch origin</pre><p>will produce a numbered series of files in the current directory, one |
| for each patch in the current branch but not in <code class="literal">origin/HEAD</code>.</p><p><code class="literal">git format-patch</code> can include an initial "cover letter". You can insert |
| commentary on individual patches after the three dash line which |
| <code class="literal">format-patch</code> places after the commit message but before the patch |
| itself. If you use <code class="literal">git notes</code> to track your cover letter material, |
| <code class="literal">git format-patch --notes</code> will include the commit’s notes in a similar |
| manner.</p><p>You can then import these into your mail client and send them by |
| hand. However, if you have a lot to send at once, you may prefer to |
| use the <a class="ulink" href="git-send-email.html" target="_top">git-send-email(1)</a> script to automate the process. |
| Consult the mailing list for your project first to determine |
| their requirements for submitting patches.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="importing-patches"></a>Importing patches to a project</h2></div></div></div><p>Git also provides a tool called <a class="ulink" href="git-am.html" target="_top">git-am(1)</a> (am stands for |
| "apply mailbox"), for importing such an emailed series of patches. |
| Just save all of the patch-containing messages, in order, into a |
| single mailbox file, say <code class="literal">patches.mbox</code>, then run</p><pre class="literallayout">$ git am -3 patches.mbox</pre><p>Git will apply each patch in order; if any conflicts are found, it |
| will stop, and you can fix the conflicts as described in |
| "<a class="link" href="#resolving-a-merge" title="Resolving a merge">Resolving a merge</a>". (The <code class="literal">-3</code> option tells |
| Git to perform a merge; if you would prefer it just to abort and |
| leave your tree and index untouched, you may omit that option.)</p><p>Once the index is updated with the results of the conflict |
| resolution, instead of creating a new commit, just run</p><pre class="literallayout">$ git am --continue</pre><p>and Git will create the commit for you and continue applying the |
| remaining patches from the mailbox.</p><p>The final result will be a series of commits, one for each patch in |
| the original mailbox, with authorship and commit log message each |
| taken from the message containing each patch.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="public-repositories"></a>Public Git repositories</h2></div></div></div><p>Another way to submit changes to a project is to tell the maintainer |
| of that project to pull the changes from your repository using |
| <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>. In the section "<a class="link" href="#getting-updates-With-git-pull" title="Getting updates with git pull">Getting updates with <code class="literal">git pull</code></a>" we described this as a way to get |
| updates from the "main" repository, but it works just as well in the |
| other direction.</p><p>If you and the maintainer both have accounts on the same machine, then |
| you can just pull changes from each other’s repositories directly; |
| commands that accept repository URLs as arguments will also accept a |
| local directory name:</p><pre class="literallayout">$ git clone /path/to/repository |
| $ git pull /path/to/other/repository</pre><p>or an ssh URL:</p><pre class="literallayout">$ git clone ssh://yourhost/~you/repository</pre><p>For projects with few developers, or for synchronizing a few private |
| repositories, this may be all you need.</p><p>However, the more common way to do this is to maintain a separate public |
| repository (usually on a different host) for others to pull changes |
| from. This is usually more convenient, and allows you to cleanly |
| separate private work in progress from publicly visible work.</p><p>You will continue to do your day-to-day work in your personal |
| repository, but periodically "push" changes from your personal |
| repository into your public repository, allowing other developers to |
| pull from that repository. So the flow of changes, in a situation |
| where there is one other developer with a public repository, looks |
| like this:</p><pre class="literallayout"> you push |
| your personal repo ------------------> your public repo |
| ^ | |
| | | |
| | you pull | they pull |
| | | |
| | | |
| | they push V |
| their public repo <------------------- their repo</pre><p>We explain how to do this in the following sections.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-a-public-repository"></a>Setting up a public repository</h3></div></div></div><p>Assume your personal repository is in the directory <code class="literal">~/proj</code>. We |
| first create a new clone of the repository and tell <code class="literal">git daemon</code> that it |
| is meant to be public:</p><pre class="literallayout">$ git clone --bare ~/proj proj.git |
| $ touch proj.git/git-daemon-export-ok</pre><p>The resulting directory proj.git contains a "bare" git repository—it is |
| just the contents of the <code class="literal">.git</code> directory, without any files checked out |
| around it.</p><p>Next, copy <code class="literal">proj.git</code> to the server where you plan to host the |
| public repository. You can use scp, rsync, or whatever is most |
| convenient.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="exporting-via-git"></a>Exporting a Git repository via the Git protocol</h3></div></div></div><p>This is the preferred method.</p><p>If someone else administers the server, they should tell you what |
| directory to put the repository in, and what <code class="literal">git://</code> URL it will |
| appear at. You can then skip to the section |
| "<a class="link" href="#pushing-changes-to-a-public-repository" title="Pushing changes to a public repository">Pushing changes to a public repository</a>", below.</p><p>Otherwise, all you need to do is start <a class="ulink" href="git-daemon.html" target="_top">git-daemon(1)</a>; it will |
| listen on port 9418. By default, it will allow access to any directory |
| that looks like a Git directory and contains the magic file |
| git-daemon-export-ok. Passing some directory paths as <code class="literal">git daemon</code> |
| arguments will further restrict the exports to those paths.</p><p>You can also run <code class="literal">git daemon</code> as an inetd service; see the |
| <a class="ulink" href="git-daemon.html" target="_top">git-daemon(1)</a> man page for details. (See especially the |
| examples section.)</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="exporting-via-http"></a>Exporting a git repository via HTTP</h3></div></div></div><p>The Git protocol gives better performance and reliability, but on a |
| host with a web server set up, HTTP exports may be simpler to set up.</p><p>All you need to do is place the newly created bare Git repository in |
| a directory that is exported by the web server, and make some |
| adjustments to give web clients some extra information they need:</p><pre class="literallayout">$ mv proj.git /home/you/public_html/proj.git |
| $ cd proj.git |
| $ git --bare update-server-info |
| $ mv hooks/post-update.sample hooks/post-update</pre><p>(For an explanation of the last two lines, see |
| <a class="ulink" href="git-update-server-info.html" target="_top">git-update-server-info(1)</a> and <a class="ulink" href="githooks.html" target="_top">githooks(5)</a>.)</p><p>Advertise the URL of <code class="literal">proj.git</code>. Anybody else should then be able to |
| clone or pull from that URL, for example with a command line like:</p><pre class="literallayout">$ git clone http://yourserver.com/~you/proj.git</pre><p>(See also |
| <a class="ulink" href="howto/setup-git-server-over-http.html" target="_top">setup-git-server-over-http</a> |
| for a slightly more sophisticated setup using WebDAV which also |
| allows pushing over HTTP.)</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="pushing-changes-to-a-public-repository"></a>Pushing changes to a public repository</h3></div></div></div><p>Note that the two techniques outlined above (exporting via |
| <a class="link" href="#exporting-via-http" title="Exporting a git repository via HTTP">http</a> or <a class="link" href="#exporting-via-git" title="Exporting a Git repository via the Git protocol">git</a>) allow other |
| maintainers to fetch your latest changes, but they do not allow write |
| access, which you will need to update the public repository with the |
| latest changes created in your private repository.</p><p>The simplest way to do this is using <a class="ulink" href="git-push.html" target="_top">git-push(1)</a> and ssh; to |
| update the remote branch named <code class="literal">master</code> with the latest state of your |
| branch named <code class="literal">master</code>, run</p><pre class="literallayout">$ git push ssh://yourserver.com/~you/proj.git master:master</pre><p>or just</p><pre class="literallayout">$ git push ssh://yourserver.com/~you/proj.git master</pre><p>As with <code class="literal">git fetch</code>, <code class="literal">git push</code> will complain if this does not result in a |
| <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>; see the following section for details on |
| handling this case.</p><p>Note that the target of a <code class="literal">push</code> is normally a |
| <a class="link" href="#def_bare_repository">bare</a> repository. You can also push to a |
| repository that has a checked-out working tree, but a push to update the |
| currently checked-out branch is denied by default to prevent confusion. |
| See the description of the receive.denyCurrentBranch option |
| in <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for details.</p><p>As with <code class="literal">git fetch</code>, you may also set up configuration options to |
| save typing; so, for example:</p><pre class="literallayout">$ git remote add public-repo ssh://yourserver.com/~you/proj.git</pre><p>adds the following to <code class="literal">.git/config</code>:</p><pre class="literallayout">[remote "public-repo"] |
| url = yourserver.com:proj.git |
| fetch = +refs/heads/*:refs/remotes/example/*</pre><p>which lets you do the same push with just</p><pre class="literallayout">$ git push public-repo master</pre><p>See the explanations of the <code class="literal">remote.<name>.url</code>, |
| <code class="literal">branch.<name>.remote</code>, and <code class="literal">remote.<name>.push</code> options in |
| <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for details.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="forcing-push"></a>What to do when a push fails</h3></div></div></div><p>If a push would not result in a <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a> of the |
| remote branch, then it will fail with an error like:</p><pre class="literallayout"> ! [rejected] master -> master (non-fast-forward) |
| error: failed to push some refs to '...' |
| hint: Updates were rejected because the tip of your current branch is behind |
| hint: its remote counterpart. Integrate the remote changes (e.g. |
| hint: 'git pull ...') before pushing again. |
| hint: See the 'Note about fast-forwards' in 'git push --help' for details.</pre><p>This can happen, for example, if you:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| use <code class="literal">git reset --hard</code> to remove already-published commits, or |
| </li><li class="listitem"> |
| use <code class="literal">git commit --amend</code> to replace already-published commits |
| (as in <a class="xref" href="#fixing-a-mistake-by-rewriting-history" title="Fixing a mistake by rewriting history">the section called “Fixing a mistake by rewriting history”</a>), or |
| </li><li class="listitem"> |
| use <code class="literal">git rebase</code> to rebase any already-published commits (as |
| in <a class="xref" href="#using-git-rebase" title="Keeping a patch series up to date using git rebase">the section called “Keeping a patch series up to date using git rebase”</a>). |
| </li></ul></div><p>You may force <code class="literal">git push</code> to perform the update anyway by preceding the |
| branch name with a plus sign:</p><pre class="literallayout">$ git push ssh://yourserver.com/~you/proj.git +master</pre><p>Note the addition of the <code class="literal">+</code> sign. Alternatively, you can use the |
| <code class="literal">-f</code> flag to force the remote update, as in:</p><pre class="literallayout">$ git push -f ssh://yourserver.com/~you/proj.git master</pre><p>Normally whenever a branch head in a public repository is modified, it |
| is modified to point to a descendant of the commit that it pointed to |
| before. By forcing a push in this situation, you break that convention. |
| (See <a class="xref" href="#problems-With-rewriting-history" title="Problems with rewriting history">the section called “Problems with rewriting history”</a>.)</p><p>Nevertheless, this is a common practice for people that need a simple |
| way to publish a work-in-progress patch series, and it is an acceptable |
| compromise as long as you warn other developers that this is how you |
| intend to manage the branch.</p><p>It’s also possible for a push to fail in this way when other people have |
| the right to push to the same repository. In that case, the correct |
| solution is to retry the push after first updating your work: either by a |
| pull, or by a fetch followed by a rebase; see the |
| <a class="link" href="#setting-up-a-shared-repository" title="Setting up a shared repository">next section</a> and |
| <a class="ulink" href="gitcvs-migration.html" target="_top">gitcvs-migration(7)</a> for more.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-a-shared-repository"></a>Setting up a shared repository</h3></div></div></div><p>Another way to collaborate is by using a model similar to that |
| commonly used in CVS, where several developers with special rights |
| all push to and pull from a single shared repository. See |
| <a class="ulink" href="gitcvs-migration.html" target="_top">gitcvs-migration(7)</a> for instructions on how to |
| set this up.</p><p>However, while there is nothing wrong with Git’s support for shared |
| repositories, this mode of operation is not generally recommended, |
| simply because the mode of collaboration that Git supports—by |
| exchanging patches and pulling from public repositories—has so many |
| advantages over the central shared repository:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| Git’s ability to quickly import and merge patches allows a |
| single maintainer to process incoming changes even at very |
| high rates. And when that becomes too much, <code class="literal">git pull</code> provides |
| an easy way for that maintainer to delegate this job to other |
| maintainers while still allowing optional review of incoming |
| changes. |
| </li><li class="listitem"> |
| Since every developer’s repository has the same complete copy |
| of the project history, no repository is special, and it is |
| trivial for another developer to take over maintenance of a |
| project, either by mutual agreement, or because a maintainer |
| becomes unresponsive or difficult to work with. |
| </li><li class="listitem"> |
| The lack of a central group of "committers" means there is |
| less need for formal decisions about who is "in" and who is |
| "out". |
| </li></ul></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-gitweb"></a>Allowing web browsing of a repository</h3></div></div></div><p>The gitweb cgi script provides users an easy way to browse your |
| project’s revisions, file contents and logs without having to install |
| Git. Features like RSS/Atom feeds and blame/annotation details may |
| optionally be enabled.</p><p>The <a class="ulink" href="git-instaweb.html" target="_top">git-instaweb(1)</a> command provides a simple way to start |
| browsing the repository using gitweb. The default server when using |
| instaweb is lighttpd.</p><p>See the file gitweb/INSTALL in the Git source tree and |
| <a class="ulink" href="gitweb.html" target="_top">gitweb(1)</a> for instructions on details setting up a permanent |
| installation with a CGI or Perl capable server.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-get-a-git-repository-with-minimal-history"></a>How to get a Git repository with minimal history</h2></div></div></div><p>A <a class="link" href="#def_shallow_clone">shallow clone</a>, with its truncated |
| history, is useful when one is interested only in recent history |
| of a project and getting full history from the upstream is |
| expensive.</p><p>A <a class="link" href="#def_shallow_clone">shallow clone</a> is created by specifying |
| the <a class="ulink" href="git-clone.html" target="_top">git-clone(1)</a> <code class="literal">--depth</code> switch. The depth can later be |
| changed with the <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> <code class="literal">--depth</code> switch, or full |
| history restored with <code class="literal">--unshallow</code>.</p><p>Merging inside a <a class="link" href="#def_shallow_clone">shallow clone</a> will work as long |
| as a merge base is in the recent history. |
| Otherwise, it will be like merging unrelated histories and may |
| have to result in huge conflicts. This limitation may make such |
| a repository unsuitable to be used in merge based workflows.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sharing-development-examples"></a>Examples</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="maintaining-topic-branches"></a>Maintaining topic branches for a Linux subsystem maintainer</h3></div></div></div><p>This describes how Tony Luck uses Git in his role as maintainer of the |
| IA64 architecture for the Linux kernel.</p><p>He uses two public branches:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| A "test" tree into which patches are initially placed so that they |
| can get some exposure when integrated with other ongoing development. |
| This tree is available to Andrew for pulling into -mm whenever he |
| wants. |
| </li><li class="listitem"> |
| A "release" tree into which tested patches are moved for final sanity |
| checking, and as a vehicle to send them upstream to Linus (by sending |
| him a "please pull" request.) |
| </li></ul></div><p>He also uses a set of temporary branches ("topic branches"), each |
| containing a logical grouping of patches.</p><p>To set this up, first create your work tree by cloning Linus’s public |
| tree:</p><pre class="literallayout">$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git work |
| $ cd work</pre><p>Linus’s tree will be stored in the remote-tracking branch named origin/master, |
| and can be updated using <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>; you can track other |
| public trees using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a> to set up a "remote" and |
| <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> to keep them up to date; see |
| <a class="xref" href="#repositories-and-branches" title="Chapter 1. Repositories and Branches">Chapter 1, <i>Repositories and Branches</i></a>.</p><p>Now create the branches in which you are going to work; these start out |
| at the current tip of origin/master branch, and should be set up (using |
| the <code class="literal">--track</code> option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>) to merge changes in from |
| Linus by default.</p><pre class="literallayout">$ git branch --track test origin/master |
| $ git branch --track release origin/master</pre><p>These can be easily kept up to date using <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>.</p><pre class="literallayout">$ git checkout test && git pull |
| $ git checkout release && git pull</pre><p>Important note! If you have any local changes in these branches, then |
| this merge will create a commit object in the history (with no local |
| changes Git will simply do a "fast-forward" merge). Many people dislike |
| the "noise" that this creates in the Linux history, so you should avoid |
| doing this capriciously in the <code class="literal">release</code> branch, as these noisy commits |
| will become part of the permanent history when you ask Linus to pull |
| from the release branch.</p><p>A few configuration variables (see <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>) can |
| make it easy to push both branches to your public tree. (See |
| <a class="xref" href="#setting-up-a-public-repository" title="Setting up a public repository">the section called “Setting up a public repository”</a>.)</p><pre class="literallayout">$ cat >> .git/config <<EOF |
| [remote "mytree"] |
| url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux.git |
| push = release |
| push = test |
| EOF</pre><p>Then you can push both the test and release trees using |
| <a class="ulink" href="git-push.html" target="_top">git-push(1)</a>:</p><pre class="literallayout">$ git push mytree</pre><p>or push just one of the test and release branches using:</p><pre class="literallayout">$ git push mytree test</pre><p>or</p><pre class="literallayout">$ git push mytree release</pre><p>Now to apply some patches from the community. Think of a short |
| snappy name for a branch to hold this patch (or related group of |
| patches), and create a new branch from a recent stable tag of |
| Linus’s branch. Picking a stable base for your branch will: |
| 1) help you: by avoiding inclusion of unrelated and perhaps lightly |
| tested changes |
| 2) help future bug hunters that use <code class="literal">git bisect</code> to find problems</p><pre class="literallayout">$ git checkout -b speed-up-spinlocks v2.6.35</pre><p>Now you apply the patch(es), run some tests, and commit the change(s). If |
| the patch is a multi-part series, then you should apply each as a separate |
| commit to this branch.</p><pre class="literallayout">$ ... patch ... test ... commit [ ... patch ... test ... commit ]*</pre><p>When you are happy with the state of this change, you can merge it into the |
| "test" branch in preparation to make it public:</p><pre class="literallayout">$ git checkout test && git merge speed-up-spinlocks</pre><p>It is unlikely that you would have any conflicts here … but you might if you |
| spent a while on this step and had also pulled new versions from upstream.</p><p>Sometime later when enough time has passed and testing done, you can pull the |
| same branch into the <code class="literal">release</code> tree ready to go upstream. This is where you |
| see the value of keeping each patch (or patch series) in its own branch. It |
| means that the patches can be moved into the <code class="literal">release</code> tree in any order.</p><pre class="literallayout">$ git checkout release && git merge speed-up-spinlocks</pre><p>After a while, you will have a number of branches, and despite the |
| well chosen names you picked for each of them, you may forget what |
| they are for, or what status they are in. To get a reminder of what |
| changes are in a specific branch, use:</p><pre class="literallayout">$ git log linux..branchname | git shortlog</pre><p>To see whether it has already been merged into the test or release branches, |
| use:</p><pre class="literallayout">$ git log test..branchname</pre><p>or</p><pre class="literallayout">$ git log release..branchname</pre><p>(If this branch has not yet been merged, you will see some log entries. |
| If it has been merged, then there will be no output.)</p><p>Once a patch completes the great cycle (moving from test to release, |
| then pulled by Linus, and finally coming back into your local |
| <code class="literal">origin/master</code> branch), the branch for this change is no longer needed. |
| You detect this when the output from:</p><pre class="literallayout">$ git log origin..branchname</pre><p>is empty. At this point the branch can be deleted:</p><pre class="literallayout">$ git branch -d branchname</pre><p>Some changes are so trivial that it is not necessary to create a separate |
| branch and then merge into each of the test and release branches. For |
| these changes, just apply directly to the <code class="literal">release</code> branch, and then |
| merge that into the <code class="literal">test</code> branch.</p><p>After pushing your work to <code class="literal">mytree</code>, you can use |
| <a class="ulink" href="git-request-pull.html" target="_top">git-request-pull(1)</a> to prepare a "please pull" request message |
| to send to Linus:</p><pre class="literallayout">$ git push mytree |
| $ git request-pull origin mytree release</pre><p>Here are some of the scripts that simplify all this even further.</p><pre class="literallayout">==== update script ==== |
| # Update a branch in my Git tree. If the branch to be updated |
| # is origin, then pull from kernel.org. Otherwise merge |
| # origin/master branch into test|release branch |
| |
| case "$1" in |
| test|release) |
| git checkout $1 && git pull . origin |
| ;; |
| origin) |
| before=$(git rev-parse refs/remotes/origin/master) |
| git fetch origin |
| after=$(git rev-parse refs/remotes/origin/master) |
| if [ $before != $after ] |
| then |
| git log $before..$after | git shortlog |
| fi |
| ;; |
| *) |
| echo "usage: $0 origin|test|release" 1>&2 |
| exit 1 |
| ;; |
| esac</pre><pre class="literallayout">==== merge script ==== |
| # Merge a branch into either the test or release branch |
| |
| pname=$0 |
| |
| usage() |
| { |
| echo "usage: $pname branch test|release" 1>&2 |
| exit 1 |
| } |
| |
| git show-ref -q --verify -- refs/heads/"$1" || { |
| echo "Can't see branch <$1>" 1>&2 |
| usage |
| } |
| |
| case "$2" in |
| test|release) |
| if [ $(git log $2..$1 | wc -c) -eq 0 ] |
| then |
| echo $1 already merged into $2 1>&2 |
| exit 1 |
| fi |
| git checkout $2 && git pull . $1 |
| ;; |
| *) |
| usage |
| ;; |
| esac</pre><pre class="literallayout">==== status script ==== |
| # report on status of my ia64 Git tree |
| |
| gb=$(tput setab 2) |
| rb=$(tput setab 1) |
| restore=$(tput setab 9) |
| |
| if [ `git rev-list test..release | wc -c` -gt 0 ] |
| then |
| echo $rb Warning: commits in release that are not in test $restore |
| git log test..release |
| fi |
| |
| for branch in `git show-ref --heads | sed 's|^.*/||'` |
| do |
| if [ $branch = test -o $branch = release ] |
| then |
| continue |
| fi |
| |
| echo -n $gb ======= $branch ====== $restore " " |
| status= |
| for ref in test release origin/master |
| do |
| if [ `git rev-list $ref..$branch | wc -c` -gt 0 ] |
| then |
| status=$status${ref:0:1} |
| fi |
| done |
| case $status in |
| trl) |
| echo $rb Need to pull into test $restore |
| ;; |
| rl) |
| echo "In test" |
| ;; |
| l) |
| echo "Waiting for linus" |
| ;; |
| "") |
| echo $rb All done $restore |
| ;; |
| *) |
| echo $rb "<$status>" $restore |
| ;; |
| esac |
| git log origin/master..$branch | git shortlog |
| done</pre></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="cleaning-up-history"></a>Chapter 5. Rewriting history and maintaining patch series</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#patch-series">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#using-git-rebase">Keeping a patch series up to date using git rebase</a></span></dt><dt><span class="section"><a href="#rewriting-one-commit">Rewriting a single commit</a></span></dt><dt><span class="section"><a href="#reordering-patch-series">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#interactive-rebase">Using interactive rebases</a></span></dt><dt><span class="section"><a href="#patch-series-tools">Other tools</a></span></dt><dt><span class="section"><a href="#problems-With-rewriting-history">Problems with rewriting history</a></span></dt><dt><span class="section"><a href="#bisect-merges">Why bisecting merge commits can be harder than bisecting linear history</a></span></dt></dl></div><p>Normally commits are only added to a project, never taken away or |
| replaced. Git is designed with this assumption, and violating it will |
| cause Git’s merge machinery (for example) to do the wrong thing.</p><p>However, there is a situation in which it can be useful to violate this |
| assumption.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="patch-series"></a>Creating the perfect patch series</h2></div></div></div><p>Suppose you are a contributor to a large project, and you want to add a |
| complicated feature, and to present it to the other developers in a way |
| that makes it easy for them to read your changes, verify that they are |
| correct, and understand why you made each change.</p><p>If you present all of your changes as a single patch (or commit), they |
| may find that it is too much to digest all at once.</p><p>If you present them with the entire history of your work, complete with |
| mistakes, corrections, and dead ends, they may be overwhelmed.</p><p>So the ideal is usually to produce a series of patches such that:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> |
| Each patch can be applied in order. |
| </li><li class="listitem"> |
| Each patch includes a single logical change, together with a |
| message explaining the change. |
| </li><li class="listitem"> |
| No patch introduces a regression: after applying any initial |
| part of the series, the resulting project still compiles and |
| works, and has no bugs that it didn’t have before. |
| </li><li class="listitem"> |
| The complete series produces the same end result as your own |
| (probably much messier!) development process did. |
| </li></ol></div><p>We will introduce some tools that can help you do this, explain how to |
| use them, and then explain some of the problems that can arise because |
| you are rewriting history.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-git-rebase"></a>Keeping a patch series up to date using git rebase</h2></div></div></div><p>Suppose that you create a branch <code class="literal">mywork</code> on a remote-tracking branch |
| <code class="literal">origin</code>, and create some commits on top of it:</p><pre class="literallayout">$ git checkout -b mywork origin |
| $ vi file.txt |
| $ git commit |
| $ vi otherfile.txt |
| $ git commit |
| ...</pre><p>You have performed no merges into mywork, so it is just a simple linear |
| sequence of patches on top of <code class="literal">origin</code>:</p><pre class="literallayout"> o--o--O <-- origin |
| \ |
| a--b--c <-- mywork</pre><p>Some more interesting work has been done in the upstream project, and |
| <code class="literal">origin</code> has advanced:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin |
| \ |
| a--b--c <-- mywork</pre><p>At this point, you could use <code class="literal">pull</code> to merge your changes back in; |
| the result would create a new merge commit, like this:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin |
| \ \ |
| a--b--c--m <-- mywork</pre><p>However, if you prefer to keep the history in mywork a simple series of |
| commits without any merges, you may instead choose to use |
| <a class="ulink" href="git-rebase.html" target="_top">git-rebase(1)</a>:</p><pre class="literallayout">$ git checkout mywork |
| $ git rebase origin</pre><p>This will remove each of your commits from mywork, temporarily saving |
| them as patches (in a directory named <code class="literal">.git/rebase-apply</code>), update mywork to |
| point at the latest version of origin, then apply each of the saved |
| patches to the new mywork. The result will look like:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin |
| \ |
| a'--b'--c' <-- mywork</pre><p>In the process, it may discover conflicts. In that case it will stop |
| and allow you to fix the conflicts; after fixing conflicts, use <code class="literal">git add</code> |
| to update the index with those contents, and then, instead of |
| running <code class="literal">git commit</code>, just run</p><pre class="literallayout">$ git rebase --continue</pre><p>and Git will continue applying the rest of the patches.</p><p>At any point you may use the <code class="literal">--abort</code> option to abort this process and |
| return mywork to the state it had before you started the rebase:</p><pre class="literallayout">$ git rebase --abort</pre><p>If you need to reorder or edit a number of commits in a branch, it may |
| be easier to use <code class="literal">git rebase -i</code>, which allows you to reorder and |
| squash commits, as well as marking them for individual editing during |
| the rebase. See <a class="xref" href="#interactive-rebase" title="Using interactive rebases">the section called “Using interactive rebases”</a> for details, and |
| <a class="xref" href="#reordering-patch-series" title="Reordering or selecting from a patch series">the section called “Reordering or selecting from a patch series”</a> for alternatives.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="rewriting-one-commit"></a>Rewriting a single commit</h2></div></div></div><p>We saw in <a class="xref" href="#fixing-a-mistake-by-rewriting-history" title="Fixing a mistake by rewriting history">the section called “Fixing a mistake by rewriting history”</a> that you can replace the |
| most recent commit using</p><pre class="literallayout">$ git commit --amend</pre><p>which will replace the old commit by a new commit incorporating your |
| changes, giving you a chance to edit the old commit message first. |
| This is useful for fixing typos in your last commit, or for adjusting |
| the patch contents of a poorly staged commit.</p><p>If you need to amend commits from deeper in your history, you can |
| use <a class="link" href="#interactive-rebase" title="Using interactive rebases">interactive rebase’s <code class="literal">edit</code> instruction</a>.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="reordering-patch-series"></a>Reordering or selecting from a patch series</h2></div></div></div><p>Sometimes you want to edit a commit deeper in your history. One |
| approach is to use <code class="literal">git format-patch</code> to create a series of patches |
| and then reset the state to before the patches:</p><pre class="literallayout">$ git format-patch origin |
| $ git reset --hard origin</pre><p>Then modify, reorder, or eliminate patches as needed before applying |
| them again with <a class="ulink" href="git-am.html" target="_top">git-am(1)</a>:</p><pre class="literallayout">$ git am *.patch</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="interactive-rebase"></a>Using interactive rebases</h2></div></div></div><p>You can also edit a patch series with an interactive rebase. This is |
| the same as <a class="link" href="#reordering-patch-series" title="Reordering or selecting from a patch series">reordering a patch series using <code class="literal">format-patch</code></a>, so use whichever interface you like best.</p><p>Rebase your current HEAD on the last commit you want to retain as-is. |
| For example, if you want to reorder the last 5 commits, use:</p><pre class="literallayout">$ git rebase -i HEAD~5</pre><p>This will open your editor with a list of steps to be taken to perform |
| your rebase.</p><pre class="literallayout">pick deadbee The oneline of this commit |
| pick fa1afe1 The oneline of the next commit |
| ... |
| |
| # Rebase c0ffeee..deadbee onto c0ffeee |
| # |
| # Commands: |
| # p, pick = use commit |
| # r, reword = use commit, but edit the commit message |
| # e, edit = use commit, but stop for amending |
| # s, squash = use commit, but meld into previous commit |
| # f, fixup = like "squash", but discard this commit's log message |
| # x, exec = run command (the rest of the line) using shell |
| # |
| # These lines can be re-ordered; they are executed from top to bottom. |
| # |
| # If you remove a line here THAT COMMIT WILL BE LOST. |
| # |
| # However, if you remove everything, the rebase will be aborted. |
| # |
| # Note that empty commits are commented out</pre><p>As explained in the comments, you can reorder commits, squash them |
| together, edit commit messages, etc. by editing the list. Once you |
| are satisfied, save the list and close your editor, and the rebase |
| will begin.</p><p>The rebase will stop where <code class="literal">pick</code> has been replaced with <code class="literal">edit</code> or |
| when a step in the list fails to mechanically resolve conflicts and |
| needs your help. When you are done editing and/or resolving conflicts |
| you can continue with <code class="literal">git rebase --continue</code>. If you decide that |
| things are getting too hairy, you can always bail out with <code class="literal">git rebase |
| --abort</code>. Even after the rebase is complete, you can still recover |
| the original branch by using the <a class="link" href="#reflogs" title="Reflogs">reflog</a>.</p><p>For a more detailed discussion of the procedure and additional tips, |
| see the "INTERACTIVE MODE" section of <a class="ulink" href="git-rebase.html" target="_top">git-rebase(1)</a>.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="patch-series-tools"></a>Other tools</h2></div></div></div><p>There are numerous other tools, such as StGit, which exist for the |
| purpose of maintaining a patch series. These are outside of the scope of |
| this manual.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="problems-With-rewriting-history"></a>Problems with rewriting history</h2></div></div></div><p>The primary problem with rewriting the history of a branch has to do |
| with merging. Suppose somebody fetches your branch and merges it into |
| their branch, with a result something like this:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin |
| \ \ |
| t--t--t--m <-- their branch:</pre><p>Then suppose you modify the last three commits:</p><pre class="literallayout"> o--o--o <-- new head of origin |
| / |
| o--o--O--o--o--o <-- old head of origin</pre><p>If we examined all this history together in one repository, it will |
| look like:</p><pre class="literallayout"> o--o--o <-- new head of origin |
| / |
| o--o--O--o--o--o <-- old head of origin |
| \ \ |
| t--t--t--m <-- their branch:</pre><p>Git has no way of knowing that the new head is an updated version of |
| the old head; it treats this situation exactly the same as it would if |
| two developers had independently done the work on the old and new heads |
| in parallel. At this point, if someone attempts to merge the new head |
| in to their branch, Git will attempt to merge together the two (old and |
| new) lines of development, instead of trying to replace the old by the |
| new. The results are likely to be unexpected.</p><p>You may still choose to publish branches whose history is rewritten, |
| and it may be useful for others to be able to fetch those branches in |
| order to examine or test them, but they should not attempt to pull such |
| branches into their own work.</p><p>For true distributed development that supports proper merging, |
| published branches should never be rewritten.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="bisect-merges"></a>Why bisecting merge commits can be harder than bisecting linear history</h2></div></div></div><p>The <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command correctly handles history that |
| includes merge commits. However, when the commit that it finds is a |
| merge commit, the user may need to work harder than usual to figure out |
| why that commit introduced a problem.</p><p>Imagine this history:</p><pre class="literallayout"> ---Z---o---X---...---o---A---C---D |
| \ / |
| o---o---Y---...---o---B</pre><p>Suppose that on the upper line of development, the meaning of one |
| of the functions that exists at Z is changed at commit X. The |
| commits from Z leading to A change both the function’s |
| implementation and all calling sites that exist at Z, as well |
| as new calling sites they add, to be consistent. There is no |
| bug at A.</p><p>Suppose that in the meantime on the lower line of development somebody |
| adds a new calling site for that function at commit Y. The |
| commits from Z leading to B all assume the old semantics of that |
| function and the callers and the callee are consistent with each |
| other. There is no bug at B, either.</p><p>Suppose further that the two development lines merge cleanly at C, |
| so no conflict resolution is required.</p><p>Nevertheless, the code at C is broken, because the callers added |
| on the lower line of development have not been converted to the new |
| semantics introduced on the upper line of development. So if all |
| you know is that D is bad, that Z is good, and that |
| <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> identifies C as the culprit, how will you |
| figure out that the problem is due to this change in semantics?</p><p>When the result of a <code class="literal">git bisect</code> is a non-merge commit, you should |
| normally be able to discover the problem by examining just that commit. |
| Developers can make this easy by breaking their changes into small |
| self-contained commits. That won’t help in the case above, however, |
| because the problem isn’t obvious from examination of any single |
| commit; instead, a global view of the development is required. To |
| make matters worse, the change in semantics in the problematic |
| function may be just one small part of the changes in the upper |
| line of development.</p><p>On the other hand, if instead of merging at C you had rebased the |
| history between Z to B on top of A, you would have gotten this |
| linear history:</p><pre class="literallayout"> ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*</pre><p>Bisecting between Z and D* would hit a single culprit commit Y*, |
| and understanding why Y* was broken would probably be easier.</p><p>Partly for this reason, many experienced Git users, even when |
| working on an otherwise merge-heavy project, keep the history |
| linear by rebasing against the latest upstream version before |
| publishing.</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="advanced-branch-management"></a>Chapter 6. Advanced branch management</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#fetching-individual-branches">Fetching individual branches</a></span></dt><dt><span class="section"><a href="#fetch-fast-forwards">git fetch and fast-forwards</a></span></dt><dt><span class="section"><a href="#forcing-fetch">Forcing git fetch to do non-fast-forward updates</a></span></dt><dt><span class="section"><a href="#remote-branch-configuration">Configuring remote-tracking branches</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetching-individual-branches"></a>Fetching individual branches</h2></div></div></div><p>Instead of using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>, you can also choose just |
| to update one branch at a time, and to store it locally under an |
| arbitrary name:</p><pre class="literallayout">$ git fetch origin todo:my-todo-work</pre><p>The first argument, <code class="literal">origin</code>, just tells Git to fetch from the |
| repository you originally cloned from. The second argument tells Git |
| to fetch the branch named <code class="literal">todo</code> from the remote repository, and to |
| store it locally under the name <code class="literal">refs/heads/my-todo-work</code>.</p><p>You can also fetch branches from other repositories; so</p><pre class="literallayout">$ git fetch git://example.com/proj.git master:example-master</pre><p>will create a new branch named <code class="literal">example-master</code> and store in it the |
| branch named <code class="literal">master</code> from the repository at the given URL. If you |
| already have a branch named example-master, it will attempt to |
| <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a> to the commit given by example.com’s |
| master branch. In more detail:</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetch-fast-forwards"></a>git fetch and fast-forwards</h2></div></div></div><p>In the previous example, when updating an existing branch, <code class="literal">git fetch</code> |
| checks to make sure that the most recent commit on the remote |
| branch is a descendant of the most recent commit on your copy of the |
| branch before updating your copy of the branch to point at the new |
| commit. Git calls this process a <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>.</p><p>A fast-forward looks something like this:</p><pre class="literallayout"> o--o--o--o <-- old head of the branch |
| \ |
| o--o--o <-- new head of the branch</pre><p>In some cases it is possible that the new head will <span class="strong"><strong>not</strong></span> actually be |
| a descendant of the old head. For example, the developer may have |
| realized she made a serious mistake, and decided to backtrack, |
| resulting in a situation like:</p><pre class="literallayout"> o--o--o--o--a--b <-- old head of the branch |
| \ |
| o--o--o <-- new head of the branch</pre><p>In this case, <code class="literal">git fetch</code> will fail, and print out a warning.</p><p>In that case, you can still force Git to update to the new head, as |
| described in the following section. However, note that in the |
| situation above this may mean losing the commits labeled <code class="literal">a</code> and <code class="literal">b</code>, |
| unless you’ve already created a reference of your own pointing to |
| them.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="forcing-fetch"></a>Forcing git fetch to do non-fast-forward updates</h2></div></div></div><p>If git fetch fails because the new head of a branch is not a |
| descendant of the old head, you may force the update with:</p><pre class="literallayout">$ git fetch git://example.com/proj.git +master:refs/remotes/example/master</pre><p>Note the addition of the <code class="literal">+</code> sign. Alternatively, you can use the <code class="literal">-f</code> |
| flag to force updates of all the fetched branches, as in:</p><pre class="literallayout">$ git fetch -f origin</pre><p>Be aware that commits that the old version of example/master pointed at |
| may be lost, as we saw in the previous section.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="remote-branch-configuration"></a>Configuring remote-tracking branches</h2></div></div></div><p>We saw above that <code class="literal">origin</code> is just a shortcut to refer to the |
| repository that you originally cloned from. This information is |
| stored in Git configuration variables, which you can see using |
| <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>:</p><pre class="literallayout">$ git config -l |
| core.repositoryformatversion=0 |
| core.filemode=true |
| core.logallrefupdates=true |
| remote.origin.url=git://git.kernel.org/pub/scm/git/git.git |
| remote.origin.fetch=+refs/heads/*:refs/remotes/origin/* |
| branch.master.remote=origin |
| branch.master.merge=refs/heads/master</pre><p>If there are other repositories that you also use frequently, you can |
| create similar configuration options to save typing; for example,</p><pre class="literallayout">$ git remote add example git://example.com/proj.git</pre><p>adds the following to <code class="literal">.git/config</code>:</p><pre class="literallayout">[remote "example"] |
| url = git://example.com/proj.git |
| fetch = +refs/heads/*:refs/remotes/example/*</pre><p>Also note that the above configuration can be performed by directly |
| editing the file <code class="literal">.git/config</code> instead of using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>.</p><p>After configuring the remote, the following three commands will do the |
| same thing:</p><pre class="literallayout">$ git fetch git://example.com/proj.git +refs/heads/*:refs/remotes/example/* |
| $ git fetch example +refs/heads/*:refs/remotes/example/* |
| $ git fetch example</pre><p>See <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for more details on the configuration |
| options mentioned above and <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> for more details on |
| the refspec syntax.</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="git-concepts"></a>Chapter 7. Git concepts</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#the-object-database">The Object Database</a></span></dt><dd><dl><dt><span class="section"><a href="#commit-object">Commit Object</a></span></dt><dt><span class="section"><a href="#tree-object">Tree Object</a></span></dt><dt><span class="section"><a href="#blob-object">Blob Object</a></span></dt><dt><span class="section"><a href="#trust">Trust</a></span></dt><dt><span class="section"><a href="#tag-object">Tag Object</a></span></dt><dt><span class="section"><a href="#pack-files">How Git stores objects efficiently: pack files</a></span></dt><dt><span class="section"><a href="#dangling-objects">Dangling objects</a></span></dt><dt><span class="section"><a href="#recovering-from-repository-corruption">Recovering from repository corruption</a></span></dt></dl></dd><dt><span class="section"><a href="#the-index">The index</a></span></dt></dl></div><p>Git is built on a small number of simple but powerful ideas. While it |
| is possible to get things done without understanding them, you will find |
| Git much more intuitive if you do.</p><p>We start with the most important, the <a class="link" href="#def_object_database">object database</a> and the <a class="link" href="#def_index">index</a>.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-object-database"></a>The Object Database</h2></div></div></div><p>We already saw in <a class="xref" href="#understanding-commits" title="Understanding History: Commits">the section called “Understanding History: Commits”</a> that all commits are stored |
| under a 40-digit "object name". In fact, all the information needed to |
| represent the history of a project is stored in objects with such names. |
| In each case the name is calculated by taking the SHA-1 hash of the |
| contents of the object. The SHA-1 hash is a cryptographic hash function. |
| What that means to us is that it is impossible to find two different |
| objects with the same name. This has a number of advantages; among |
| others:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| Git can quickly determine whether two objects are identical or not, |
| just by comparing names. |
| </li><li class="listitem"> |
| Since object names are computed the same way in every repository, the |
| same content stored in two repositories will always be stored under |
| the same name. |
| </li><li class="listitem"> |
| Git can detect errors when it reads an object, by checking that the |
| object’s name is still the SHA-1 hash of its contents. |
| </li></ul></div><p>(See <a class="xref" href="#object-details" title="Object storage format">the section called “Object storage format”</a> for the details of the object formatting and |
| SHA-1 calculation.)</p><p>There are four different types of objects: "blob", "tree", "commit", and |
| "tag".</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| A <a class="link" href="#def_blob_object">"blob" object</a> is used to store file data. |
| </li><li class="listitem"> |
| A <a class="link" href="#def_tree_object">"tree" object</a> ties one or more |
| "blob" objects into a directory structure. In addition, a tree object |
| can refer to other tree objects, thus creating a directory hierarchy. |
| </li><li class="listitem"> |
| A <a class="link" href="#def_commit_object">"commit" object</a> ties such directory hierarchies |
| together into a <a class="link" href="#def_DAG">directed acyclic graph</a> of revisions—each |
| commit contains the object name of exactly one tree designating the |
| directory hierarchy at the time of the commit. In addition, a commit |
| refers to "parent" commit objects that describe the history of how we |
| arrived at that directory hierarchy. |
| </li><li class="listitem"> |
| A <a class="link" href="#def_tag_object">"tag" object</a> symbolically identifies and can be |
| used to sign other objects. It contains the object name and type of |
| another object, a symbolic name (of course!) and, optionally, a |
| signature. |
| </li></ul></div><p>The object types in some more detail:</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="commit-object"></a>Commit Object</h3></div></div></div><p>The "commit" object links a physical state of a tree with a description |
| of how we got there and why. Use the <code class="literal">--pretty=raw</code> option to |
| <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> or <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> to examine your favorite |
| commit:</p><pre class="literallayout">$ git show -s --pretty=raw 2be7fcb476 |
| commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4 |
| tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf |
| parent 257a84d9d02e90447b149af58b271c19405edb6a |
| author Dave Watson <dwatson@mimvista.com> 1187576872 -0400 |
| committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700 |
| |
| Fix misspelling of 'suppress' in docs |
| |
| Signed-off-by: Junio C Hamano <gitster@pobox.com></pre><p>As you can see, a commit is defined by:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| a tree: The SHA-1 name of a tree object (as defined below), representing |
| the contents of a directory at a certain point in time. |
| </li><li class="listitem"> |
| parent(s): The SHA-1 name(s) of some number of commits which represent the |
| immediately previous step(s) in the history of the project. The |
| example above has one parent; merge commits may have more than |
| one. A commit with no parents is called a "root" commit, and |
| represents the initial revision of a project. Each project must have |
| at least one root. A project can also have multiple roots, though |
| that isn’t common (or necessarily a good idea). |
| </li><li class="listitem"> |
| an author: The name of the person responsible for this change, together |
| with its date. |
| </li><li class="listitem"> |
| a committer: The name of the person who actually created the commit, |
| with the date it was done. This may be different from the author, for |
| example, if the author was someone who wrote a patch and emailed it |
| to the person who used it to create the commit. |
| </li><li class="listitem"> |
| a comment describing this commit. |
| </li></ul></div><p>Note that a commit does not itself contain any information about what |
| actually changed; all changes are calculated by comparing the contents |
| of the tree referred to by this commit with the trees associated with |
| its parents. In particular, Git does not attempt to record file renames |
| explicitly, though it can identify cases where the existence of the same |
| file data at changing paths suggests a rename. (See, for example, the |
| <code class="literal">-M</code> option to <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>).</p><p>A commit is usually created by <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a>, which creates a |
| commit whose parent is normally the current HEAD, and whose tree is |
| taken from the content currently stored in the index.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="tree-object"></a>Tree Object</h3></div></div></div><p>The ever-versatile <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command can also be used to |
| examine tree objects, but <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a> will give you more |
| details:</p><pre class="literallayout">$ git ls-tree fb3a8bdd0ce |
| 100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore |
| 100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap |
| 100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING |
| 040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation |
| 100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN |
| 100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL |
| 100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile |
| 100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README |
| ...</pre><p>As you can see, a tree object contains a list of entries, each with a |
| mode, object type, SHA-1 name, and name, sorted by name. It represents |
| the contents of a single directory tree.</p><p>The object type may be a blob, representing the contents of a file, or |
| another tree, representing the contents of a subdirectory. Since trees |
| and blobs, like all other objects, are named by the SHA-1 hash of their |
| contents, two trees have the same SHA-1 name if and only if their |
| contents (including, recursively, the contents of all subdirectories) |
| are identical. This allows Git to quickly determine the differences |
| between two related tree objects, since it can ignore any entries with |
| identical object names.</p><p>(Note: in the presence of submodules, trees may also have commits as |
| entries. See <a class="xref" href="#submodules" title="Chapter 8. Submodules">Chapter 8, <i>Submodules</i></a> for documentation.)</p><p>Note that the files all have mode 644 or 755: Git actually only pays |
| attention to the executable bit.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="blob-object"></a>Blob Object</h3></div></div></div><p>You can use <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> to examine the contents of a blob; take, |
| for example, the blob in the entry for <code class="literal">COPYING</code> from the tree above:</p><pre class="literallayout">$ git show 6ff87c4664 |
| |
| Note that the only valid version of the GPL as far as this project |
| is concerned is _this_ particular version of the license (ie v2, not |
| v2.2 or v3.x or whatever), unless explicitly otherwise stated. |
| ...</pre><p>A "blob" object is nothing but a binary blob of data. It doesn’t refer |
| to anything else or have attributes of any kind.</p><p>Since the blob is entirely defined by its data, if two files in a |
| directory tree (or in multiple different versions of the repository) |
| have the same contents, they will share the same blob object. The object |
| is totally independent of its location in the directory tree, and |
| renaming a file does not change the object that file is associated with.</p><p>Note that any tree or blob object can be examined using |
| <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> with the <revision>:<path> syntax. This can |
| sometimes be useful for browsing the contents of a tree that is not |
| currently checked out.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="trust"></a>Trust</h3></div></div></div><p>If you receive the SHA-1 name of a blob from one source, and its contents |
| from another (possibly untrusted) source, you can still trust that those |
| contents are correct as long as the SHA-1 name agrees. This is because |
| the SHA-1 is designed so that it is infeasible to find different contents |
| that produce the same hash.</p><p>Similarly, you need only trust the SHA-1 name of a top-level tree object |
| to trust the contents of the entire directory that it refers to, and if |
| you receive the SHA-1 name of a commit from a trusted source, then you |
| can easily verify the entire history of commits reachable through |
| parents of that commit, and all of those contents of the trees referred |
| to by those commits.</p><p>So to introduce some real trust in the system, the only thing you need |
| to do is to digitally sign just <span class="emphasis"><em>one</em></span> special note, which includes the |
| name of a top-level commit. Your digital signature shows others |
| that you trust that commit, and the immutability of the history of |
| commits tells others that they can trust the whole history.</p><p>In other words, you can easily validate a whole archive by just |
| sending out a single email that tells the people the name (SHA-1 hash) |
| of the top commit, and digitally sign that email using something |
| like GPG/PGP.</p><p>To assist in this, Git also provides the tag object…</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="tag-object"></a>Tag Object</h3></div></div></div><p>A tag object contains an object, object type, tag name, the name of the |
| person ("tagger") who created the tag, and a message, which may contain |
| a signature, as can be seen using <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a>:</p><pre class="literallayout">$ git cat-file tag v1.5.0 |
| object 437b1b20df4b356c9342dac8d38849f24ef44f27 |
| type commit |
| tag v1.5.0 |
| tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000 |
| |
| GIT 1.5.0 |
| -----BEGIN PGP SIGNATURE----- |
| Version: GnuPG v1.4.6 (GNU/Linux) |
| |
| iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui |
| nLE/L9aUXdWeTFPron96DLA= |
| =2E+0 |
| -----END PGP SIGNATURE-----</pre><p>See the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> command to learn how to create and verify tag |
| objects. (Note that <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> can also be used to create |
| "lightweight tags", which are not tag objects at all, but just simple |
| references whose names begin with <code class="literal">refs/tags/</code>).</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="pack-files"></a>How Git stores objects efficiently: pack files</h3></div></div></div><p>Newly created objects are initially created in a file named after the |
| object’s SHA-1 hash (stored in <code class="literal">.git/objects</code>).</p><p>Unfortunately this system becomes inefficient once a project has a |
| lot of objects. Try this on an old project:</p><pre class="literallayout">$ git count-objects |
| 6930 objects, 47620 kilobytes</pre><p>The first number is the number of objects which are kept in |
| individual files. The second is the amount of space taken up by |
| those "loose" objects.</p><p>You can save space and make Git faster by moving these loose objects in |
| to a "pack file", which stores a group of objects in an efficient |
| compressed format; the details of how pack files are formatted can be |
| found in <a class="ulink" href="technical/pack-format.html" target="_top">pack format</a>.</p><p>To put the loose objects into a pack, just run git repack:</p><pre class="literallayout">$ git repack |
| Counting objects: 6020, done. |
| Delta compression using up to 4 threads. |
| Compressing objects: 100% (6020/6020), done. |
| Writing objects: 100% (6020/6020), done. |
| Total 6020 (delta 4070), reused 0 (delta 0)</pre><p>This creates a single "pack file" in .git/objects/pack/ |
| containing all currently unpacked objects. You can then run</p><pre class="literallayout">$ git prune</pre><p>to remove any of the "loose" objects that are now contained in the |
| pack. This will also remove any unreferenced objects (which may be |
| created when, for example, you use <code class="literal">git reset</code> to remove a commit). |
| You can verify that the loose objects are gone by looking at the |
| <code class="literal">.git/objects</code> directory or by running</p><pre class="literallayout">$ git count-objects |
| 0 objects, 0 kilobytes</pre><p>Although the object files are gone, any commands that refer to those |
| objects will work exactly as they did before.</p><p>The <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a> command performs packing, pruning, and more for |
| you, so is normally the only high-level command you need.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dangling-objects"></a>Dangling objects</h3></div></div></div><p>The <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a> command will sometimes complain about dangling |
| objects. They are not a problem.</p><p>The most common cause of dangling objects is that you’ve rebased a |
| branch, or you have pulled from somebody else who rebased a branch—see |
| <a class="xref" href="#cleaning-up-history" title="Chapter 5. Rewriting history and maintaining patch series">Chapter 5, <i>Rewriting history and maintaining patch series</i></a>. In that case, the old head of the original |
| branch still exists, as does everything it pointed to. The branch |
| pointer itself just doesn’t, since you replaced it with another one.</p><p>There are also other situations that cause dangling objects. For |
| example, a "dangling blob" may arise because you did a <code class="literal">git add</code> of a |
| file, but then, before you actually committed it and made it part of the |
| bigger picture, you changed something else in that file and committed |
| that <span class="strong"><strong>updated</strong></span> thing—the old state that you added originally ends up |
| not being pointed to by any commit or tree, so it’s now a dangling blob |
| object.</p><p>Similarly, when the "recursive" merge strategy runs, and finds that |
| there are criss-cross merges and thus more than one merge base (which is |
| fairly unusual, but it does happen), it will generate one temporary |
| midway tree (or possibly even more, if you had lots of criss-crossing |
| merges and more than two merge bases) as a temporary internal merge |
| base, and again, those are real objects, but the end result will not end |
| up pointing to them, so they end up "dangling" in your repository.</p><p>Generally, dangling objects aren’t anything to worry about. They can |
| even be very useful: if you screw something up, the dangling objects can |
| be how you recover your old tree (say, you did a rebase, and realized |
| that you really didn’t want to—you can look at what dangling objects |
| you have, and decide to reset your head to some old dangling state).</p><p>For commits, you can just use:</p><pre class="literallayout">$ gitk <dangling-commit-sha-goes-here> --not --all</pre><p>This asks for all the history reachable from the given commit but not |
| from any branch, tag, or other reference. If you decide it’s something |
| you want, you can always create a new reference to it, e.g.,</p><pre class="literallayout">$ git branch recovered-branch <dangling-commit-sha-goes-here></pre><p>For blobs and trees, you can’t do the same, but you can still examine |
| them. You can just do</p><pre class="literallayout">$ git show <dangling-blob/tree-sha-goes-here></pre><p>to show what the contents of the blob were (or, for a tree, basically |
| what the <code class="literal">ls</code> for that directory was), and that may give you some idea |
| of what the operation was that left that dangling object.</p><p>Usually, dangling blobs and trees aren’t very interesting. They’re |
| almost always the result of either being a half-way mergebase (the blob |
| will often even have the conflict markers from a merge in it, if you |
| have had conflicting merges that you fixed up by hand), or simply |
| because you interrupted a <code class="literal">git fetch</code> with ^C or something like that, |
| leaving <span class="emphasis"><em>some</em></span> of the new objects in the object database, but just |
| dangling and useless.</p><p>Anyway, once you are sure that you’re not interested in any dangling |
| state, you can just prune all unreachable objects:</p><pre class="literallayout">$ git prune</pre><p>and they’ll be gone. (You should only run <code class="literal">git prune</code> on a quiescent |
| repository—it’s kind of like doing a filesystem fsck recovery: you |
| don’t want to do that while the filesystem is mounted. |
| <code class="literal">git prune</code> is designed not to cause any harm in such cases of concurrent |
| accesses to a repository but you might receive confusing or scary messages.)</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="recovering-from-repository-corruption"></a>Recovering from repository corruption</h3></div></div></div><p>By design, Git treats data trusted to it with caution. However, even in |
| the absence of bugs in Git itself, it is still possible that hardware or |
| operating system errors could corrupt data.</p><p>The first defense against such problems is backups. You can back up a |
| Git directory using clone, or just using cp, tar, or any other backup |
| mechanism.</p><p>As a last resort, you can search for the corrupted objects and attempt |
| to replace them by hand. Back up your repository before attempting this |
| in case you corrupt things even more in the process.</p><p>We’ll assume that the problem is a single missing or corrupted blob, |
| which is sometimes a solvable problem. (Recovering missing trees and |
| especially commits is <span class="strong"><strong>much</strong></span> harder).</p><p>Before starting, verify that there is corruption, and figure out where |
| it is with <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a>; this may be time-consuming.</p><p>Assume the output looks like this:</p><pre class="literallayout">$ git fsck --full --no-dangling |
| broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8 |
| to blob 4b9458b3786228369c63936db65827de3cc06200 |
| missing blob 4b9458b3786228369c63936db65827de3cc06200</pre><p>Now you know that blob 4b9458b3 is missing, and that the tree 2d9263c6 |
| points to it. If you could find just one copy of that missing blob |
| object, possibly in some other repository, you could move it into |
| <code class="literal">.git/objects/4b/9458b3...</code> and be done. Suppose you can’t. You can |
| still examine the tree that pointed to it with <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>, |
| which might output something like:</p><pre class="literallayout">$ git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8 |
| 100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8 .gitignore |
| 100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap |
| 100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING |
| ... |
| 100644 blob 4b9458b3786228369c63936db65827de3cc06200 myfile |
| ...</pre><p>So now you know that the missing blob was the data for a file named |
| <code class="literal">myfile</code>. And chances are you can also identify the directory—let’s |
| say it’s in <code class="literal">somedirectory</code>. If you’re lucky the missing copy might be |
| the same as the copy you have checked out in your working tree at |
| <code class="literal">somedirectory/myfile</code>; you can test whether that’s right with |
| <a class="ulink" href="git-hash-object.html" target="_top">git-hash-object(1)</a>:</p><pre class="literallayout">$ git hash-object -w somedirectory/myfile</pre><p>which will create and store a blob object with the contents of |
| somedirectory/myfile, and output the SHA-1 of that object. if you’re |
| extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in |
| which case you’ve guessed right, and the corruption is fixed!</p><p>Otherwise, you need more information. How do you tell which version of |
| the file has been lost?</p><p>The easiest way to do this is with:</p><pre class="literallayout">$ git log --raw --all --full-history -- somedirectory/myfile</pre><p>Because you’re asking for raw output, you’ll now get something like</p><pre class="literallayout">commit abc |
| Author: |
| Date: |
| ... |
| :100644 100644 4b9458b newsha M somedirectory/myfile |
| |
| |
| commit xyz |
| Author: |
| Date: |
| |
| ... |
| :100644 100644 oldsha 4b9458b M somedirectory/myfile</pre><p>This tells you that the immediately following version of the file was |
| "newsha", and that the immediately preceding version was "oldsha". |
| You also know the commit messages that went with the change from oldsha |
| to 4b9458b and with the change from 4b9458b to newsha.</p><p>If you’ve been committing small enough changes, you may now have a good |
| shot at reconstructing the contents of the in-between state 4b9458b.</p><p>If you can do that, you can now recreate the missing object with</p><pre class="literallayout">$ git hash-object -w <recreated-file></pre><p>and your repository is good again!</p><p>(Btw, you could have ignored the <code class="literal">fsck</code>, and started with doing a</p><pre class="literallayout">$ git log --raw --all</pre><p>and just looked for the sha of the missing object (4b9458b) in that |
| whole thing. It’s up to you—Git does <span class="strong"><strong>have</strong></span> a lot of information, it is |
| just missing one particular blob version.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-index"></a>The index</h2></div></div></div><p>The index is a binary file (generally kept in <code class="literal">.git/index</code>) containing a |
| sorted list of path names, each with permissions and the SHA-1 of a blob |
| object; <a class="ulink" href="git-ls-files.html" target="_top">git-ls-files(1)</a> can show you the contents of the index:</p><pre class="literallayout">$ git ls-files --stage |
| 100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore |
| 100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap |
| 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING |
| 100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore |
| 100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile |
| ... |
| 100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h |
| 100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c |
| 100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h</pre><p>Note that in older documentation you may see the index called the |
| "current directory cache" or just the "cache". It has three important |
| properties:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p class="simpara"> |
| The index contains all the information necessary to generate a single |
| (uniquely determined) tree object. |
| </p><p class="simpara">For example, running <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> generates this tree object |
| from the index, stores it in the object database, and uses it as the |
| tree object associated with the new commit.</p></li><li class="listitem"><p class="simpara"> |
| The index enables fast comparisons between the tree object it defines |
| and the working tree. |
| </p><p class="simpara">It does this by storing some additional data for each entry (such as |
| the last modified time). This data is not displayed above, and is not |
| stored in the created tree object, but it can be used to determine |
| quickly which files in the working directory differ from what was |
| stored in the index, and thus save Git from having to read all of the |
| data from such files to look for changes.</p></li><li class="listitem"><p class="simpara"> |
| It can efficiently represent information about merge conflicts |
| between different tree objects, allowing each pathname to be |
| associated with sufficient information about the trees involved that |
| you can create a three-way merge between them. |
| </p><p class="simpara">We saw in <a class="xref" href="#conflict-resolution" title="Getting conflict-resolution help during a merge">the section called “Getting conflict-resolution help during a merge”</a> that during a merge the index can |
| store multiple versions of a single file (called "stages"). The third |
| column in the <a class="ulink" href="git-ls-files.html" target="_top">git-ls-files(1)</a> output above is the stage |
| number, and will take on values other than 0 for files with merge |
| conflicts.</p></li></ol></div><p>The index is thus a sort of temporary staging area, which is filled with |
| a tree which you are in the process of working on.</p><p>If you blow the index away entirely, you generally haven’t lost any |
| information as long as you have the name of the tree that it described.</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="submodules"></a>Chapter 8. Submodules</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#_pitfalls_with_submodules">Pitfalls with submodules</a></span></dt></dl></div><p>Large projects are often composed of smaller, self-contained modules. For |
| example, an embedded Linux distribution’s source tree would include every |
| piece of software in the distribution with some local modifications; a movie |
| player might need to build against a specific, known-working version of a |
| decompression library; several independent programs might all share the same |
| build scripts.</p><p>With centralized revision control systems this is often accomplished by |
| including every module in one single repository. Developers can check out |
| all modules or only the modules they need to work with. They can even modify |
| files across several modules in a single commit while moving things around |
| or updating APIs and translations.</p><p>Git does not allow partial checkouts, so duplicating this approach in Git |
| would force developers to keep a local copy of modules they are not |
| interested in touching. Commits in an enormous checkout would be slower |
| than you’d expect as Git would have to scan every directory for changes. |
| If modules have a lot of local history, clones would take forever.</p><p>On the plus side, distributed revision control systems can much better |
| integrate with external sources. In a centralized model, a single arbitrary |
| snapshot of the external project is exported from its own revision control |
| and then imported into the local revision control on a vendor branch. All |
| the history is hidden. With distributed revision control you can clone the |
| entire external history and much more easily follow development and re-merge |
| local changes.</p><p>Git’s submodule support allows a repository to contain, as a subdirectory, a |
| checkout of an external project. Submodules maintain their own identity; |
| the submodule support just stores the submodule repository location and |
| commit ID, so other developers who clone the containing project |
| ("superproject") can easily clone all the submodules at the same revision. |
| Partial checkouts of the superproject are possible: you can tell Git to |
| clone none, some or all of the submodules.</p><p>The <a class="ulink" href="git-submodule.html" target="_top">git-submodule(1)</a> command is available since Git 1.5.3. Users |
| with Git 1.5.2 can look up the submodule commits in the repository and |
| manually check them out; earlier versions won’t recognize the submodules at |
| all.</p><p>To see how submodule support works, create four example |
| repositories that can be used later as a submodule:</p><pre class="literallayout">$ mkdir ~/git |
| $ cd ~/git |
| $ for i in a b c d |
| do |
| mkdir $i |
| cd $i |
| git init |
| echo "module $i" > $i.txt |
| git add $i.txt |
| git commit -m "Initial commit, submodule $i" |
| cd .. |
| done</pre><p>Now create the superproject and add all the submodules:</p><pre class="literallayout">$ mkdir super |
| $ cd super |
| $ git init |
| $ for i in a b c d |
| do |
| git submodule add ~/git/$i $i |
| done</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Do not use local URLs here if you plan to publish your superproject!</p></div><p>See what files <code class="literal">git submodule</code> created:</p><pre class="literallayout">$ ls -a |
| . .. .git .gitmodules a b c d</pre><p>The <code class="literal">git submodule add <repo> <path></code> command does a couple of things:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| It clones the submodule from <code class="literal"><repo></code> to the given <code class="literal"><path></code> under the |
| current directory and by default checks out the master branch. |
| </li><li class="listitem"> |
| It adds the submodule’s clone path to the <a class="ulink" href="gitmodules.html" target="_top">gitmodules(5)</a> file and |
| adds this file to the index, ready to be committed. |
| </li><li class="listitem"> |
| It adds the submodule’s current commit ID to the index, ready to be |
| committed. |
| </li></ul></div><p>Commit the superproject:</p><pre class="literallayout">$ git commit -m "Add submodules a, b, c and d."</pre><p>Now clone the superproject:</p><pre class="literallayout">$ cd .. |
| $ git clone super cloned |
| $ cd cloned</pre><p>The submodule directories are there, but they’re empty:</p><pre class="literallayout">$ ls -a a |
| . .. |
| $ git submodule status |
| -d266b9873ad50488163457f025db7cdd9683d88b a |
| -e81d457da15309b4fef4249aba9b50187999670d b |
| -c1536a972b9affea0f16e0680ba87332dc059146 c |
| -d96249ff5d57de5de093e6baff9e0aafa5276a74 d</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The commit object names shown above would be different for you, but they |
| should match the HEAD commit object names of your repositories. You can check |
| it by running <code class="literal">git ls-remote ../a</code>.</p></div><p>Pulling down the submodules is a two-step process. First run <code class="literal">git submodule |
| init</code> to add the submodule repository URLs to <code class="literal">.git/config</code>:</p><pre class="literallayout">$ git submodule init</pre><p>Now use <code class="literal">git submodule update</code> to clone the repositories and check out the |
| commits specified in the superproject:</p><pre class="literallayout">$ git submodule update |
| $ cd a |
| $ ls -a |
| . .. .git a.txt</pre><p>One major difference between <code class="literal">git submodule update</code> and <code class="literal">git submodule add</code> is |
| that <code class="literal">git submodule update</code> checks out a specific commit, rather than the tip |
| of a branch. It’s like checking out a tag: the head is detached, so you’re not |
| working on a branch.</p><pre class="literallayout">$ git branch |
| * (detached from d266b98) |
| master</pre><p>If you want to make a change within a submodule and you have a detached head, |
| then you should create or checkout a branch, make your changes, publish the |
| change within the submodule, and then update the superproject to reference the |
| new commit:</p><pre class="literallayout">$ git checkout master</pre><p>or</p><pre class="literallayout">$ git checkout -b fix-up</pre><p>then</p><pre class="literallayout">$ echo "adding a line again" >> a.txt |
| $ git commit -a -m "Updated the submodule from within the superproject." |
| $ git push |
| $ cd .. |
| $ git diff |
| diff --git a/a b/a |
| index d266b98..261dfac 160000 |
| --- a/a |
| +++ b/a |
| @@ -1 +1 @@ |
| -Subproject commit d266b9873ad50488163457f025db7cdd9683d88b |
| +Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24 |
| $ git add a |
| $ git commit -m "Updated submodule a." |
| $ git push</pre><p>You have to run <code class="literal">git submodule update</code> after <code class="literal">git pull</code> if you want to update |
| submodules, too.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_pitfalls_with_submodules"></a>Pitfalls with submodules</h2></div></div></div><p>Always publish the submodule change before publishing the change to the |
| superproject that references it. If you forget to publish the submodule change, |
| others won’t be able to clone the repository:</p><pre class="literallayout">$ cd ~/git/super/a |
| $ echo i added another line to this file >> a.txt |
| $ git commit -a -m "doing it wrong this time" |
| $ cd .. |
| $ git add a |
| $ git commit -m "Updated submodule a again." |
| $ git push |
| $ cd ~/git/cloned |
| $ git pull |
| $ git submodule update |
| error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git. |
| Did you forget to 'git add'? |
| Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a'</pre><p>In older Git versions it could be easily forgotten to commit new or modified |
| files in a submodule, which silently leads to similar problems as not pushing |
| the submodule changes. Starting with Git 1.7.0 both <code class="literal">git status</code> and <code class="literal">git diff</code> |
| in the superproject show submodules as modified when they contain new or |
| modified files to protect against accidentally committing such a state. <code class="literal">git |
| diff</code> will also add a <code class="literal">-dirty</code> to the work tree side when generating patch |
| output or used with the <code class="literal">--submodule</code> option:</p><pre class="literallayout">$ git diff |
| diff --git a/sub b/sub |
| --- a/sub |
| +++ b/sub |
| @@ -1 +1 @@ |
| -Subproject commit 3f356705649b5d566d97ff843cf193359229a453 |
| +Subproject commit 3f356705649b5d566d97ff843cf193359229a453-dirty |
| $ git diff --submodule |
| Submodule sub 3f35670..3f35670-dirty:</pre><p>You also should not rewind branches in a submodule beyond commits that were |
| ever recorded in any superproject.</p><p>It’s not safe to run <code class="literal">git submodule update</code> if you’ve made and committed |
| changes within a submodule without checking out a branch first. They will be |
| silently overwritten:</p><pre class="literallayout">$ cat a.txt |
| module a |
| $ echo line added from private2 >> a.txt |
| $ git commit -a -m "line added inside private2" |
| $ cd .. |
| $ git submodule update |
| Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b' |
| $ cd a |
| $ cat a.txt |
| module a</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The changes are still visible in the submodule’s reflog.</p></div><p>If you have uncommitted changes in your submodule working tree, <code class="literal">git |
| submodule update</code> will not overwrite them. Instead, you get the usual |
| warning about not being able switch from a dirty branch.</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="low-level-operations"></a>Chapter 9. Low-level Git operations</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#object-manipulation">Object access and manipulation</a></span></dt><dt><span class="section"><a href="#the-workflow">The Workflow</a></span></dt><dd><dl><dt><span class="section"><a href="#working-directory-to-index">working directory → index</a></span></dt><dt><span class="section"><a href="#index-to-object-database">index → object database</a></span></dt><dt><span class="section"><a href="#object-database-to-index">object database → index</a></span></dt><dt><span class="section"><a href="#index-to-working-directory">index → working directory</a></span></dt><dt><span class="section"><a href="#tying-it-all-together">Tying it all together</a></span></dt></dl></dd><dt><span class="section"><a href="#examining-the-data">Examining the data</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees">Merging multiple trees</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees-2">Merging multiple trees, continued</a></span></dt></dl></div><p>Many of the higher-level commands were originally implemented as shell |
| scripts using a smaller core of low-level Git commands. These can still |
| be useful when doing unusual things with Git, or just as a way to |
| understand its inner workings.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="object-manipulation"></a>Object access and manipulation</h2></div></div></div><p>The <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a> command can show the contents of any object, |
| though the higher-level <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> is usually more useful.</p><p>The <a class="ulink" href="git-commit-tree.html" target="_top">git-commit-tree(1)</a> command allows constructing commits with |
| arbitrary parents and trees.</p><p>A tree can be created with <a class="ulink" href="git-write-tree.html" target="_top">git-write-tree(1)</a> and its data can be |
| accessed by <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>. Two trees can be compared with |
| <a class="ulink" href="git-diff-tree.html" target="_top">git-diff-tree(1)</a>.</p><p>A tag is created with <a class="ulink" href="git-mktag.html" target="_top">git-mktag(1)</a>, and the signature can be |
| verified by <a class="ulink" href="git-verify-tag.html" target="_top">git-verify-tag(1)</a>, though it is normally simpler to |
| use <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> for both.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-workflow"></a>The Workflow</h2></div></div></div><p>High-level operations such as <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a>, |
| <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a> and <a class="ulink" href="git-reset.html" target="_top">git-reset(1)</a> work by moving data |
| between the working tree, the index, and the object database. Git |
| provides low-level operations which perform each of these steps |
| individually.</p><p>Generally, all Git operations work on the index file. Some operations |
| work <span class="strong"><strong>purely</strong></span> on the index file (showing the current state of the |
| index), but most operations move data between the index file and either |
| the database or the working directory. Thus there are four main |
| combinations:</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="working-directory-to-index"></a>working directory → index</h3></div></div></div><p>The <a class="ulink" href="git-update-index.html" target="_top">git-update-index(1)</a> command updates the index with |
| information from the working directory. You generally update the |
| index information by just specifying the filename you want to update, |
| like so:</p><pre class="literallayout">$ git update-index filename</pre><p>but to avoid common mistakes with filename globbing etc., the command |
| will not normally add totally new entries or remove old entries, |
| i.e. it will normally just update existing cache entries.</p><p>To tell Git that yes, you really do realize that certain files no |
| longer exist, or that new files should be added, you |
| should use the <code class="literal">--remove</code> and <code class="literal">--add</code> flags respectively.</p><p>NOTE! A <code class="literal">--remove</code> flag does <span class="emphasis"><em>not</em></span> mean that subsequent filenames will |
| necessarily be removed: if the files still exist in your directory |
| structure, the index will be updated with their new status, not |
| removed. The only thing <code class="literal">--remove</code> means is that update-index will be |
| considering a removed file to be a valid thing, and if the file really |
| does not exist any more, it will update the index accordingly.</p><p>As a special case, you can also do <code class="literal">git update-index --refresh</code>, which |
| will refresh the "stat" information of each index to match the current |
| stat information. It will <span class="emphasis"><em>not</em></span> update the object status itself, and |
| it will only update the fields that are used to quickly test whether |
| an object still matches its old backing store object.</p><p>The previously introduced <a class="ulink" href="git-add.html" target="_top">git-add(1)</a> is just a wrapper for |
| <a class="ulink" href="git-update-index.html" target="_top">git-update-index(1)</a>.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="index-to-object-database"></a>index → object database</h3></div></div></div><p>You write your current index file to a "tree" object with the program</p><pre class="literallayout">$ git write-tree</pre><p>that doesn’t come with any options—it will just write out the |
| current index into the set of tree objects that describe that state, |
| and it will return the name of the resulting top-level tree. You can |
| use that tree to re-generate the index at any time by going in the |
| other direction:</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="object-database-to-index"></a>object database → index</h3></div></div></div><p>You read a "tree" file from the object database, and use that to |
| populate (and overwrite—don’t do this if your index contains any |
| unsaved state that you might want to restore later!) your current |
| index. Normal operation is just</p><pre class="literallayout">$ git read-tree <SHA-1 of tree></pre><p>and your index file will now be equivalent to the tree that you saved |
| earlier. However, that is only your <span class="emphasis"><em>index</em></span> file: your working |
| directory contents have not been modified.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="index-to-working-directory"></a>index → working directory</h3></div></div></div><p>You update your working directory from the index by "checking out" |
| files. This is not a very common operation, since normally you’d just |
| keep your files updated, and rather than write to your working |
| directory, you’d tell the index files about the changes in your |
| working directory (i.e. <code class="literal">git update-index</code>).</p><p>However, if you decide to jump to a new version, or check out somebody |
| else’s version, or just restore a previous tree, you’d populate your |
| index file with read-tree, and then you need to check out the result |
| with</p><pre class="literallayout">$ git checkout-index filename</pre><p>or, if you want to check out all of the index, use <code class="literal">-a</code>.</p><p>NOTE! <code class="literal">git checkout-index</code> normally refuses to overwrite old files, so |
| if you have an old version of the tree already checked out, you will |
| need to use the <code class="literal">-f</code> flag (<span class="emphasis"><em>before</em></span> the <code class="literal">-a</code> flag or the filename) to |
| <span class="emphasis"><em>force</em></span> the checkout.</p><p>Finally, there are a few odds and ends which are not purely moving |
| from one representation to the other:</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="tying-it-all-together"></a>Tying it all together</h3></div></div></div><p>To commit a tree you have instantiated with <code class="literal">git write-tree</code>, you’d |
| create a "commit" object that refers to that tree and the history |
| behind it—most notably the "parent" commits that preceded it in |
| history.</p><p>Normally a "commit" has one parent: the previous state of the tree |
| before a certain change was made. However, sometimes it can have two |
| or more parent commits, in which case we call it a "merge", due to the |
| fact that such a commit brings together ("merges") two or more |
| previous states represented by other commits.</p><p>In other words, while a "tree" represents a particular directory state |
| of a working directory, a "commit" represents that state in time, |
| and explains how we got there.</p><p>You create a commit object by giving it the tree that describes the |
| state at the time of the commit, and a list of parents:</p><pre class="literallayout">$ git commit-tree <tree> -p <parent> [(-p <parent2>)...]</pre><p>and then giving the reason for the commit on stdin (either through |
| redirection from a pipe or file, or by just typing it at the tty).</p><p><code class="literal">git commit-tree</code> will return the name of the object that represents |
| that commit, and you should save it away for later use. Normally, |
| you’d commit a new <code class="literal">HEAD</code> state, and while Git doesn’t care where you |
| save the note about that state, in practice we tend to just write the |
| result to the file pointed at by <code class="literal">.git/HEAD</code>, so that we can always see |
| what the last committed state was.</p><p>Here is a picture that illustrates how various pieces fit together:</p><pre class="literallayout"> commit-tree |
| commit obj |
| +----+ |
| | | |
| | | |
| V V |
| +-----------+ |
| | Object DB | |
| | Backing | |
| | Store | |
| +-----------+ |
| ^ |
| write-tree | | |
| tree obj | | |
| | | read-tree |
| | | tree obj |
| V |
| +-----------+ |
| | Index | |
| | "cache" | |
| +-----------+ |
| update-index ^ |
| blob obj | | |
| | | |
| checkout-index -u | | checkout-index |
| stat | | blob obj |
| V |
| +-----------+ |
| | Working | |
| | Directory | |
| +-----------+</pre></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="examining-the-data"></a>Examining the data</h2></div></div></div><p>You can examine the data represented in the object database and the |
| index with various helper tools. For every object, you can use |
| <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a> to examine details about the |
| object:</p><pre class="literallayout">$ git cat-file -t <objectname></pre><p>shows the type of the object, and once you have the type (which is |
| usually implicit in where you find the object), you can use</p><pre class="literallayout">$ git cat-file blob|tree|commit|tag <objectname></pre><p>to show its contents. NOTE! Trees have binary content, and as a result |
| there is a special helper for showing that content, called |
| <code class="literal">git ls-tree</code>, which turns the binary content into a more easily |
| readable form.</p><p>It’s especially instructive to look at "commit" objects, since those |
| tend to be small and fairly self-explanatory. In particular, if you |
| follow the convention of having the top commit name in <code class="literal">.git/HEAD</code>, |
| you can do</p><pre class="literallayout">$ git cat-file commit HEAD</pre><p>to see what the top commit was.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging-multiple-trees"></a>Merging multiple trees</h2></div></div></div><p>Git can help you perform a three-way merge, which can in turn be |
| used for a many-way merge by repeating the merge procedure several |
| times. The usual situation is that you only do one three-way merge |
| (reconciling two lines of history) and commit the result, but if |
| you like to, you can merge several branches in one go.</p><p>To perform a three-way merge, you start with the two commits you |
| want to merge, find their closest common parent (a third commit), |
| and compare the trees corresponding to these three commits.</p><p>To get the "base" for the merge, look up the common parent of two |
| commits:</p><pre class="literallayout">$ git merge-base <commit1> <commit2></pre><p>This prints the name of a commit they are both based on. You should |
| now look up the tree objects of those commits, which you can easily |
| do with</p><pre class="literallayout">$ git cat-file commit <commitname> | head -1</pre><p>since the tree object information is always the first line in a commit |
| object.</p><p>Once you know the three trees you are going to merge (the one "original" |
| tree, aka the common tree, and the two "result" trees, aka the branches |
| you want to merge), you do a "merge" read into the index. This will |
| complain if it has to throw away your old index contents, so you should |
| make sure that you’ve committed those—in fact you would normally |
| always do a merge against your last commit (which should thus match what |
| you have in your current index anyway).</p><p>To do the merge, do</p><pre class="literallayout">$ git read-tree -m -u <origtree> <yourtree> <targettree></pre><p>which will do all trivial merge operations for you directly in the |
| index file, and you can just write the result out with |
| <code class="literal">git write-tree</code>.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging-multiple-trees-2"></a>Merging multiple trees, continued</h2></div></div></div><p>Sadly, many merges aren’t trivial. If there are files that have |
| been added, moved or removed, or if both branches have modified the |
| same file, you will be left with an index tree that contains "merge |
| entries" in it. Such an index tree can <span class="emphasis"><em>NOT</em></span> be written out to a tree |
| object, and you will have to resolve any such merge clashes using |
| other tools before you can write out the result.</p><p>You can examine such index state with <code class="literal">git ls-files --unmerged</code> |
| command. An example:</p><pre class="literallayout">$ git read-tree -m $orig HEAD $target |
| $ git ls-files --unmerged |
| 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c |
| 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c |
| 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c</pre><p>Each line of the <code class="literal">git ls-files --unmerged</code> output begins with |
| the blob mode bits, blob SHA-1, <span class="emphasis"><em>stage number</em></span>, and the |
| filename. The <span class="emphasis"><em>stage number</em></span> is Git’s way to say which tree it |
| came from: stage 1 corresponds to the <code class="literal">$orig</code> tree, stage 2 to |
| the <code class="literal">HEAD</code> tree, and stage 3 to the <code class="literal">$target</code> tree.</p><p>Earlier we said that trivial merges are done inside |
| <code class="literal">git read-tree -m</code>. For example, if the file did not change |
| from <code class="literal">$orig</code> to <code class="literal">HEAD</code> or <code class="literal">$target</code>, or if the file changed |
| from <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> the same way, |
| obviously the final outcome is what is in <code class="literal">HEAD</code>. What the |
| above example shows is that file <code class="literal">hello.c</code> was changed from |
| <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> in a different way. |
| You could resolve this by running your favorite 3-way merge |
| program, e.g. <code class="literal">diff3</code>, <code class="literal">merge</code>, or Git’s own merge-file, on |
| the blob objects from these three stages yourself, like this:</p><pre class="literallayout">$ git cat-file blob 263414f >hello.c~1 |
| $ git cat-file blob 06fa6a2 >hello.c~2 |
| $ git cat-file blob cc44c73 >hello.c~3 |
| $ git merge-file hello.c~2 hello.c~1 hello.c~3</pre><p>This would leave the merge result in <code class="literal">hello.c~2</code> file, along |
| with conflict markers if there are conflicts. After verifying |
| the merge result makes sense, you can tell Git what the final |
| merge result for this file is by:</p><pre class="literallayout">$ mv -f hello.c~2 hello.c |
| $ git update-index hello.c</pre><p>When a path is in the "unmerged" state, running <code class="literal">git update-index</code> for |
| that path tells Git to mark the path resolved.</p><p>The above is the description of a Git merge at the lowest level, |
| to help you understand what conceptually happens under the hood. |
| In practice, nobody, not even Git itself, runs <code class="literal">git cat-file</code> three times |
| for this. There is a <code class="literal">git merge-index</code> program that extracts the |
| stages to temporary files and calls a "merge" script on it:</p><pre class="literallayout">$ git merge-index git-merge-one-file hello.c</pre><p>and that is what higher level <code class="literal">git merge -s resolve</code> is implemented with.</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="hacking-git"></a>Chapter 10. Hacking Git</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#object-details">Object storage format</a></span></dt><dt><span class="section"><a href="#birdview-on-the-source-code">A birds-eye view of Git’s source code</a></span></dt></dl></div><p>This chapter covers internal details of the Git implementation which |
| probably only Git developers need to understand.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="object-details"></a>Object storage format</h2></div></div></div><p>All objects have a statically determined "type" which identifies the |
| format of the object (i.e. how it is used, and how it can refer to other |
| objects). There are currently four different object types: "blob", |
| "tree", "commit", and "tag".</p><p>Regardless of object type, all objects share the following |
| characteristics: they are all deflated with zlib, and have a header |
| that not only specifies their type, but also provides size information |
| about the data in the object. It’s worth noting that the SHA-1 hash |
| that is used to name the object is the hash of the original data |
| plus this header, so <code class="literal">sha1sum</code> <span class="emphasis"><em>file</em></span> does not match the object name |
| for <span class="emphasis"><em>file</em></span>.</p><p>As a result, the general consistency of an object can always be tested |
| independently of the contents or the type of the object: all objects can |
| be validated by verifying that (a) their hashes match the content of the |
| file and (b) the object successfully inflates to a stream of bytes that |
| forms a sequence of |
| <code class="literal"><ascii type without space> + <space> + <ascii decimal size> + |
| <byte\0> + <binary object data></code>.</p><p>The structured objects can further have their structure and |
| connectivity to other objects verified. This is generally done with |
| the <code class="literal">git fsck</code> program, which generates a full dependency graph |
| of all objects, and verifies their internal consistency (in addition |
| to just verifying their superficial consistency through the hash).</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="birdview-on-the-source-code"></a>A birds-eye view of Git’s source code</h2></div></div></div><p>It is not always easy for new developers to find their way through Git’s |
| source code. This section gives you a little guidance to show where to |
| start.</p><p>A good place to start is with the contents of the initial commit, with:</p><pre class="literallayout">$ git checkout e83c5163</pre><p>The initial revision lays the foundation for almost everything Git has |
| today, but is small enough to read in one sitting.</p><p>Note that terminology has changed since that revision. For example, the |
| README in that revision uses the word "changeset" to describe what we |
| now call a <a class="link" href="#def_commit_object">commit</a>.</p><p>Also, we do not call it "cache" any more, but rather "index"; however, the |
| file is still called <code class="literal">cache.h</code>. Remark: Not much reason to change it now, |
| especially since there is no good single name for it anyway, because it is |
| basically <span class="emphasis"><em>the</em></span> header file which is included by <span class="emphasis"><em>all</em></span> of Git’s C sources.</p><p>If you grasp the ideas in that initial commit, you should check out a |
| more recent version and skim <code class="literal">cache.h</code>, <code class="literal">object.h</code> and <code class="literal">commit.h</code>.</p><p>In the early days, Git (in the tradition of UNIX) was a bunch of programs |
| which were extremely simple, and which you used in scripts, piping the |
| output of one into another. This turned out to be good for initial |
| development, since it was easier to test new things. However, recently |
| many of these parts have become builtins, and some of the core has been |
| "libified", i.e. put into libgit.a for performance, portability reasons, |
| and to avoid code duplication.</p><p>By now, you know what the index is (and find the corresponding data |
| structures in <code class="literal">cache.h</code>), and that there are just a couple of object types |
| (blobs, trees, commits and tags) which inherit their common structure from |
| <code class="literal">struct object</code>, which is their first member (and thus, you can cast e.g. |
| <code class="literal">(struct object *)commit</code> to achieve the <span class="emphasis"><em>same</em></span> as <code class="literal">&commit->object</code>, i.e. |
| get at the object name and flags).</p><p>Now is a good point to take a break to let this information sink in.</p><p>Next step: get familiar with the object naming. Read <a class="xref" href="#naming-commits" title="Naming commits">the section called “Naming commits”</a>. |
| There are quite a few ways to name an object (and not only revisions!). |
| All of these are handled in <code class="literal">sha1_name.c</code>. Just have a quick look at |
| the function <code class="literal">get_sha1()</code>. A lot of the special handling is done by |
| functions like <code class="literal">get_sha1_basic()</code> or the likes.</p><p>This is just to get you into the groove for the most libified part of Git: |
| the revision walker.</p><p>Basically, the initial version of <code class="literal">git log</code> was a shell script:</p><pre class="literallayout">$ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | \ |
| LESS=-S ${PAGER:-less}</pre><p>What does this mean?</p><p><code class="literal">git rev-list</code> is the original version of the revision walker, which |
| <span class="emphasis"><em>always</em></span> printed a list of revisions to stdout. It is still functional, |
| and needs to, since most new Git commands start out as scripts using |
| <code class="literal">git rev-list</code>.</p><p><code class="literal">git rev-parse</code> is not as important any more; it was only used to filter out |
| options that were relevant for the different plumbing commands that were |
| called by the script.</p><p>Most of what <code class="literal">git rev-list</code> did is contained in <code class="literal">revision.c</code> and |
| <code class="literal">revision.h</code>. It wraps the options in a struct named <code class="literal">rev_info</code>, which |
| controls how and what revisions are walked, and more.</p><p>The original job of <code class="literal">git rev-parse</code> is now taken by the function |
| <code class="literal">setup_revisions()</code>, which parses the revisions and the common command-line |
| options for the revision walker. This information is stored in the struct |
| <code class="literal">rev_info</code> for later consumption. You can do your own command-line option |
| parsing after calling <code class="literal">setup_revisions()</code>. After that, you have to call |
| <code class="literal">prepare_revision_walk()</code> for initialization, and then you can get the |
| commits one by one with the function <code class="literal">get_revision()</code>.</p><p>If you are interested in more details of the revision walking process, |
| just have a look at the first implementation of <code class="literal">cmd_log()</code>; call |
| <code class="literal">git show v1.3.0~155^2~4</code> and scroll down to that function (note that you |
| no longer need to call <code class="literal">setup_pager()</code> directly).</p><p>Nowadays, <code class="literal">git log</code> is a builtin, which means that it is <span class="emphasis"><em>contained</em></span> in the |
| command <code class="literal">git</code>. The source side of a builtin is</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| a function called <code class="literal">cmd_<bla></code>, typically defined in <code class="literal">builtin/<bla.c></code> |
| (note that older versions of Git used to have it in <code class="literal">builtin-<bla>.c</code> |
| instead), and declared in <code class="literal">builtin.h</code>. |
| </li><li class="listitem"> |
| an entry in the <code class="literal">commands[]</code> array in <code class="literal">git.c</code>, and |
| </li><li class="listitem"> |
| an entry in <code class="literal">BUILTIN_OBJECTS</code> in the <code class="literal">Makefile</code>. |
| </li></ul></div><p>Sometimes, more than one builtin is contained in one source file. For |
| example, <code class="literal">cmd_whatchanged()</code> and <code class="literal">cmd_log()</code> both reside in <code class="literal">builtin/log.c</code>, |
| since they share quite a bit of code. In that case, the commands which are |
| <span class="emphasis"><em>not</em></span> named like the <code class="literal">.c</code> file in which they live have to be listed in |
| <code class="literal">BUILT_INS</code> in the <code class="literal">Makefile</code>.</p><p><code class="literal">git log</code> looks more complicated in C than it does in the original script, |
| but that allows for a much greater flexibility and performance.</p><p>Here again it is a good point to take a pause.</p><p>Lesson three is: study the code. Really, it is the best way to learn about |
| the organization of Git (after you know the basic concepts).</p><p>So, think about something which you are interested in, say, "how can I |
| access a blob just knowing the object name of it?". The first step is to |
| find a Git command with which you can do it. In this example, it is either |
| <code class="literal">git show</code> or <code class="literal">git cat-file</code>.</p><p>For the sake of clarity, let’s stay with <code class="literal">git cat-file</code>, because it</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| is plumbing, and |
| </li><li class="listitem"> |
| was around even in the initial commit (it literally went only through |
| some 20 revisions as <code class="literal">cat-file.c</code>, was renamed to <code class="literal">builtin/cat-file.c</code> |
| when made a builtin, and then saw less than 10 versions). |
| </li></ul></div><p>So, look into <code class="literal">builtin/cat-file.c</code>, search for <code class="literal">cmd_cat_file()</code> and look what |
| it does.</p><pre class="literallayout"> git_config(git_default_config); |
| if (argc != 3) |
| usage("git cat-file [-t|-s|-e|-p|<type>] <sha1>"); |
| if (get_sha1(argv[2], sha1)) |
| die("Not a valid object name %s", argv[2]);</pre><p>Let’s skip over the obvious details; the only really interesting part |
| here is the call to <code class="literal">get_sha1()</code>. It tries to interpret <code class="literal">argv[2]</code> as an |
| object name, and if it refers to an object which is present in the current |
| repository, it writes the resulting SHA-1 into the variable <code class="literal">sha1</code>.</p><p>Two things are interesting here:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| <code class="literal">get_sha1()</code> returns 0 on <span class="emphasis"><em>success</em></span>. This might surprise some new |
| Git hackers, but there is a long tradition in UNIX to return different |
| negative numbers in case of different errors—and 0 on success. |
| </li><li class="listitem"> |
| the variable <code class="literal">sha1</code> in the function signature of <code class="literal">get_sha1()</code> is <code class="literal">unsigned |
| char *</code>, but is actually expected to be a pointer to <code class="literal">unsigned |
| char[20]</code>. This variable will contain the 160-bit SHA-1 of the given |
| commit. Note that whenever a SHA-1 is passed as <code class="literal">unsigned char *</code>, it |
| is the binary representation, as opposed to the ASCII representation in |
| hex characters, which is passed as <code class="literal">char *</code>. |
| </li></ul></div><p>You will see both of these things throughout the code.</p><p>Now, for the meat:</p><pre class="literallayout"> case 0: |
| buf = read_object_with_reference(sha1, argv[1], &size, NULL);</pre><p>This is how you read a blob (actually, not only a blob, but any type of |
| object). To know how the function <code class="literal">read_object_with_reference()</code> actually |
| works, find the source code for it (something like <code class="literal">git grep |
| read_object_with | grep ":[a-z]"</code> in the Git repository), and read |
| the source.</p><p>To find out how the result can be used, just read on in <code class="literal">cmd_cat_file()</code>:</p><pre class="literallayout"> write_or_die(1, buf, size);</pre><p>Sometimes, you do not know where to look for a feature. In many such cases, |
| it helps to search through the output of <code class="literal">git log</code>, and then <code class="literal">git show</code> the |
| corresponding commit.</p><p>Example: If you know that there was some test case for <code class="literal">git bundle</code>, but |
| do not remember where it was (yes, you <span class="emphasis"><em>could</em></span> <code class="literal">git grep bundle t/</code>, but that |
| does not illustrate the point!):</p><pre class="literallayout">$ git log --no-merges t/</pre><p>In the pager (<code class="literal">less</code>), just search for "bundle", go a few lines back, |
| and see that it is in commit 18449ab0. Now just copy this object name, |
| and paste it into the command line</p><pre class="literallayout">$ git show 18449ab0</pre><p>Voila.</p><p>Another example: Find out what to do in order to make some script a |
| builtin:</p><pre class="literallayout">$ git log --no-merges --diff-filter=A builtin/*.c</pre><p>You see, Git is actually the best tool to find out about the source of Git |
| itself!</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="glossary"></a>Chapter 11. Git Glossary</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#git-explained">Git explained</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="git-explained"></a>Git explained</h2></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term"> |
| <a name="def_alternate_object_database"></a>alternate object database |
| </span></dt><dd> |
| Via the alternates mechanism, a <a class="link" href="#def_repository">repository</a> |
| can inherit part of its <a class="link" href="#def_object_database">object database</a> |
| from another object database, which is called an "alternate". |
| </dd><dt><span class="term"> |
| <a name="def_bare_repository"></a>bare repository |
| </span></dt><dd> |
| A bare repository is normally an appropriately |
| named <a class="link" href="#def_directory">directory</a> with a <code class="literal">.git</code> suffix that does not |
| have a locally checked-out copy of any of the files under |
| revision control. That is, all of the Git |
| administrative and control files that would normally be present in the |
| hidden <code class="literal">.git</code> sub-directory are directly present in the |
| <code class="literal">repository.git</code> directory instead, |
| and no other files are present and checked out. Usually publishers of |
| public repositories make bare repositories available. |
| </dd><dt><span class="term"> |
| <a name="def_blob_object"></a>blob object |
| </span></dt><dd> |
| Untyped <a class="link" href="#def_object">object</a>, e.g. the contents of a file. |
| </dd><dt><span class="term"> |
| <a name="def_branch"></a>branch |
| </span></dt><dd> |
| A "branch" is an active line of development. The most recent |
| <a class="link" href="#def_commit">commit</a> on a branch is referred to as the tip of |
| that branch. The tip of the branch is referenced by a branch |
| <a class="link" href="#def_head">head</a>, which moves forward as additional development |
| is done on the branch. A single Git |
| <a class="link" href="#def_repository">repository</a> can track an arbitrary number of |
| branches, but your <a class="link" href="#def_working_tree">working tree</a> is |
| associated with just one of them (the "current" or "checked out" |
| branch), and <a class="link" href="#def_HEAD">HEAD</a> points to that branch. |
| </dd><dt><span class="term"> |
| <a name="def_cache"></a>cache |
| </span></dt><dd> |
| Obsolete for: <a class="link" href="#def_index">index</a>. |
| </dd><dt><span class="term"> |
| <a name="def_chain"></a>chain |
| </span></dt><dd> |
| A list of objects, where each <a class="link" href="#def_object">object</a> in the list contains |
| a reference to its successor (for example, the successor of a |
| <a class="link" href="#def_commit">commit</a> could be one of its <a class="link" href="#def_parent">parents</a>). |
| </dd><dt><span class="term"> |
| <a name="def_changeset"></a>changeset |
| </span></dt><dd> |
| BitKeeper/cvsps speak for "<a class="link" href="#def_commit">commit</a>". Since Git does not |
| store changes, but states, it really does not make sense to use the term |
| "changesets" with Git. |
| </dd><dt><span class="term"> |
| <a name="def_checkout"></a>checkout |
| </span></dt><dd> |
| The action of updating all or part of the |
| <a class="link" href="#def_working_tree">working tree</a> with a <a class="link" href="#def_tree_object">tree object</a> |
| or <a class="link" href="#def_blob_object">blob</a> from the |
| <a class="link" href="#def_object_database">object database</a>, and updating the |
| <a class="link" href="#def_index">index</a> and <a class="link" href="#def_HEAD">HEAD</a> if the whole working tree has |
| been pointed at a new <a class="link" href="#def_branch">branch</a>. |
| </dd><dt><span class="term"> |
| <a name="def_cherry-picking"></a>cherry-picking |
| </span></dt><dd> |
| In <a class="link" href="#def_SCM">SCM</a> jargon, "cherry pick" means to choose a subset of |
| changes out of a series of changes (typically commits) and record them |
| as a new series of changes on top of a different codebase. In Git, this is |
| performed by the "git cherry-pick" command to extract the change introduced |
| by an existing <a class="link" href="#def_commit">commit</a> and to record it based on the tip |
| of the current <a class="link" href="#def_branch">branch</a> as a new commit. |
| </dd><dt><span class="term"> |
| <a name="def_clean"></a>clean |
| </span></dt><dd> |
| A <a class="link" href="#def_working_tree">working tree</a> is clean, if it |
| corresponds to the <a class="link" href="#def_revision">revision</a> referenced by the current |
| <a class="link" href="#def_head">head</a>. Also see "<a class="link" href="#def_dirty">dirty</a>". |
| </dd><dt><span class="term"> |
| <a name="def_commit"></a>commit |
| </span></dt><dd><p class="simpara"> |
| As a noun: A single point in the |
| Git history; the entire history of a project is represented as a |
| set of interrelated commits. The word "commit" is often |
| used by Git in the same places other revision control systems |
| use the words "revision" or "version". Also used as a short |
| hand for <a class="link" href="#def_commit_object">commit object</a>. |
| </p><p class="simpara">As a verb: The action of storing a new snapshot of the project’s |
| state in the Git history, by creating a new commit representing the current |
| state of the <a class="link" href="#def_index">index</a> and advancing <a class="link" href="#def_HEAD">HEAD</a> |
| to point at the new commit.</p></dd><dt><span class="term"> |
| <a name="def_commit_object"></a>commit object |
| </span></dt><dd> |
| An <a class="link" href="#def_object">object</a> which contains the information about a |
| particular <a class="link" href="#def_revision">revision</a>, such as <a class="link" href="#def_parent">parents</a>, committer, |
| author, date and the <a class="link" href="#def_tree_object">tree object</a> which corresponds |
| to the top <a class="link" href="#def_directory">directory</a> of the stored |
| revision. |
| </dd><dt><span class="term"> |
| <a name="def_commit-ish"></a>commit-ish (also committish) |
| </span></dt><dd> |
| A <a class="link" href="#def_commit_object">commit object</a> or an |
| <a class="link" href="#def_object">object</a> that can be recursively dereferenced to |
| a commit object. |
| The following are all commit-ishes: |
| a commit object, |
| a <a class="link" href="#def_tag_object">tag object</a> that points to a commit |
| object, |
| a tag object that points to a tag object that points to a |
| commit object, |
| etc. |
| </dd><dt><span class="term"> |
| <a name="def_core_git"></a>core Git |
| </span></dt><dd> |
| Fundamental data structures and utilities of Git. Exposes only limited |
| source code management tools. |
| </dd><dt><span class="term"> |
| <a name="def_DAG"></a>DAG |
| </span></dt><dd> |
| Directed acyclic graph. The <a class="link" href="#def_commit_object">commit objects</a> form a |
| directed acyclic graph, because they have parents (directed), and the |
| graph of commit objects is acyclic (there is no <a class="link" href="#def_chain">chain</a> |
| which begins and ends with the same <a class="link" href="#def_object">object</a>). |
| </dd><dt><span class="term"> |
| <a name="def_dangling_object"></a>dangling object |
| </span></dt><dd> |
| An <a class="link" href="#def_unreachable_object">unreachable object</a> which is not |
| <a class="link" href="#def_reachable">reachable</a> even from other unreachable objects; a |
| dangling object has no references to it from any |
| reference or <a class="link" href="#def_object">object</a> in the <a class="link" href="#def_repository">repository</a>. |
| </dd><dt><span class="term"> |
| <a name="def_detached_HEAD"></a>detached HEAD |
| </span></dt><dd><p class="simpara"> |
| Normally the <a class="link" href="#def_HEAD">HEAD</a> stores the name of a |
| <a class="link" href="#def_branch">branch</a>, and commands that operate on the |
| history HEAD represents operate on the history leading to the |
| tip of the branch the HEAD points at. However, Git also |
| allows you to <a class="link" href="#def_checkout">check out</a> an arbitrary |
| <a class="link" href="#def_commit">commit</a> that isn’t necessarily the tip of any |
| particular branch. The HEAD in such a state is called |
| "detached". |
| </p><p class="simpara">Note that commands that operate on the history of the current branch |
| (e.g. <code class="literal">git commit</code> to build a new history on top of it) still work |
| while the HEAD is detached. They update the HEAD to point at the tip |
| of the updated history without affecting any branch. Commands that |
| update or inquire information <span class="emphasis"><em>about</em></span> the current branch (e.g. <code class="literal">git |
| branch --set-upstream-to</code> that sets what remote-tracking branch the |
| current branch integrates with) obviously do not work, as there is no |
| (real) current branch to ask about in this state.</p></dd><dt><span class="term"> |
| <a name="def_directory"></a>directory |
| </span></dt><dd> |
| The list you get with "ls" :-) |
| </dd><dt><span class="term"> |
| <a name="def_dirty"></a>dirty |
| </span></dt><dd> |
| A <a class="link" href="#def_working_tree">working tree</a> is said to be "dirty" if |
| it contains modifications which have not been <a class="link" href="#def_commit">committed</a> to the current |
| <a class="link" href="#def_branch">branch</a>. |
| </dd><dt><span class="term"> |
| <a name="def_evil_merge"></a>evil merge |
| </span></dt><dd> |
| An evil merge is a <a class="link" href="#def_merge">merge</a> that introduces changes that |
| do not appear in any <a class="link" href="#def_parent">parent</a>. |
| </dd><dt><span class="term"> |
| <a name="def_fast_forward"></a>fast-forward |
| </span></dt><dd> |
| A fast-forward is a special type of <a class="link" href="#def_merge">merge</a> where you have a |
| <a class="link" href="#def_revision">revision</a> and you are "merging" another |
| <a class="link" href="#def_branch">branch</a>'s changes that happen to be a descendant of what |
| you have. In such a case, you do not make a new <a class="link" href="#def_merge">merge</a> |
| <a class="link" href="#def_commit">commit</a> but instead just update to his |
| revision. This will happen frequently on a |
| <a class="link" href="#def_remote_tracking_branch">remote-tracking branch</a> of a remote |
| <a class="link" href="#def_repository">repository</a>. |
| </dd><dt><span class="term"> |
| <a name="def_fetch"></a>fetch |
| </span></dt><dd> |
| Fetching a <a class="link" href="#def_branch">branch</a> means to get the |
| branch’s <a class="link" href="#def_head_ref">head ref</a> from a remote |
| <a class="link" href="#def_repository">repository</a>, to find out which objects are |
| missing from the local <a class="link" href="#def_object_database">object database</a>, |
| and to get them, too. See also <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>. |
| </dd><dt><span class="term"> |
| <a name="def_file_system"></a>file system |
| </span></dt><dd> |
| Linus Torvalds originally designed Git to be a user space file system, |
| i.e. the infrastructure to hold files and directories. That ensured the |
| efficiency and speed of Git. |
| </dd><dt><span class="term"> |
| <a name="def_git_archive"></a>Git archive |
| </span></dt><dd> |
| Synonym for <a class="link" href="#def_repository">repository</a> (for arch people). |
| </dd><dt><span class="term"> |
| <a name="def_gitfile"></a>gitfile |
| </span></dt><dd> |
| A plain file <code class="literal">.git</code> at the root of a working tree that |
| points at the directory that is the real repository. |
| </dd><dt><span class="term"> |
| <a name="def_grafts"></a>grafts |
| </span></dt><dd><p class="simpara"> |
| Grafts enables two otherwise different lines of development to be joined |
| together by recording fake ancestry information for commits. This way |
| you can make Git pretend the set of <a class="link" href="#def_parent">parents</a> a <a class="link" href="#def_commit">commit</a> has |
| is different from what was recorded when the commit was |
| created. Configured via the <code class="literal">.git/info/grafts</code> file. |
| </p><p class="simpara">Note that the grafts mechanism is outdated and can lead to problems |
| transferring objects between repositories; see <a class="ulink" href="git-replace.html" target="_top">git-replace(1)</a> |
| for a more flexible and robust system to do the same thing.</p></dd><dt><span class="term"> |
| <a name="def_hash"></a>hash |
| </span></dt><dd> |
| In Git’s context, synonym for <a class="link" href="#def_object_name">object name</a>. |
| </dd><dt><span class="term"> |
| <a name="def_head"></a>head |
| </span></dt><dd> |
| A <a class="link" href="#def_ref">named reference</a> to the <a class="link" href="#def_commit">commit</a> at the tip of a |
| <a class="link" href="#def_branch">branch</a>. Heads are stored in a file in |
| <code class="literal">$GIT_DIR/refs/heads/</code> directory, except when using packed refs. (See |
| <a class="ulink" href="git-pack-refs.html" target="_top">git-pack-refs(1)</a>.) |
| </dd><dt><span class="term"> |
| <a name="def_HEAD"></a>HEAD |
| </span></dt><dd> |
| The current <a class="link" href="#def_branch">branch</a>. In more detail: Your <a class="link" href="#def_working_tree">working tree</a> is normally derived from the state of the tree |
| referred to by HEAD. HEAD is a reference to one of the |
| <a class="link" href="#def_head">heads</a> in your repository, except when using a |
| <a class="link" href="#def_detached_HEAD">detached HEAD</a>, in which case it directly |
| references an arbitrary commit. |
| </dd><dt><span class="term"> |
| <a name="def_head_ref"></a>head ref |
| </span></dt><dd> |
| A synonym for <a class="link" href="#def_head">head</a>. |
| </dd><dt><span class="term"> |
| <a name="def_hook"></a>hook |
| </span></dt><dd> |
| During the normal execution of several Git commands, call-outs are made |
| to optional scripts that allow a developer to add functionality or |
| checking. Typically, the hooks allow for a command to be pre-verified |
| and potentially aborted, and allow for a post-notification after the |
| operation is done. The hook scripts are found in the |
| <code class="literal">$GIT_DIR/hooks/</code> directory, and are enabled by simply |
| removing the <code class="literal">.sample</code> suffix from the filename. In earlier versions |
| of Git you had to make them executable. |
| </dd><dt><span class="term"> |
| <a name="def_index"></a>index |
| </span></dt><dd> |
| A collection of files with stat information, whose contents are stored |
| as objects. The index is a stored version of your |
| <a class="link" href="#def_working_tree">working tree</a>. Truth be told, it can also contain a second, and even |
| a third version of a working tree, which are used |
| when <a class="link" href="#def_merge">merging</a>. |
| </dd><dt><span class="term"> |
| <a name="def_index_entry"></a>index entry |
| </span></dt><dd> |
| The information regarding a particular file, stored in the |
| <a class="link" href="#def_index">index</a>. An index entry can be unmerged, if a |
| <a class="link" href="#def_merge">merge</a> was started, but not yet finished (i.e. if |
| the index contains multiple versions of that file). |
| </dd><dt><span class="term"> |
| <a name="def_master"></a>master |
| </span></dt><dd> |
| The default development <a class="link" href="#def_branch">branch</a>. Whenever you |
| create a Git <a class="link" href="#def_repository">repository</a>, a branch named |
| "master" is created, and becomes the active branch. In most |
| cases, this contains the local development, though that is |
| purely by convention and is not required. |
| </dd><dt><span class="term"> |
| <a name="def_merge"></a>merge |
| </span></dt><dd><p class="simpara"> |
| As a verb: To bring the contents of another |
| <a class="link" href="#def_branch">branch</a> (possibly from an external |
| <a class="link" href="#def_repository">repository</a>) into the current branch. In the |
| case where the merged-in branch is from a different repository, |
| this is done by first <a class="link" href="#def_fetch">fetching</a> the remote branch |
| and then merging the result into the current branch. This |
| combination of fetch and merge operations is called a |
| <a class="link" href="#def_pull">pull</a>. Merging is performed by an automatic process |
| that identifies changes made since the branches diverged, and |
| then applies all those changes together. In cases where changes |
| conflict, manual intervention may be required to complete the |
| merge. |
| </p><p class="simpara">As a noun: unless it is a <a class="link" href="#def_fast_forward">fast-forward</a>, a |
| successful merge results in the creation of a new <a class="link" href="#def_commit">commit</a> |
| representing the result of the merge, and having as |
| <a class="link" href="#def_parent">parents</a> the tips of the merged <a class="link" href="#def_branch">branches</a>. |
| This commit is referred to as a "merge commit", or sometimes just a |
| "merge".</p></dd><dt><span class="term"> |
| <a name="def_object"></a>object |
| </span></dt><dd> |
| The unit of storage in Git. It is uniquely identified by the |
| <a class="link" href="#def_SHA1">SHA-1</a> of its contents. Consequently, an |
| object can not be changed. |
| </dd><dt><span class="term"> |
| <a name="def_object_database"></a>object database |
| </span></dt><dd> |
| Stores a set of "objects", and an individual <a class="link" href="#def_object">object</a> is |
| identified by its <a class="link" href="#def_object_name">object name</a>. The objects usually |
| live in <code class="literal">$GIT_DIR/objects/</code>. |
| </dd><dt><span class="term"> |
| <a name="def_object_identifier"></a>object identifier |
| </span></dt><dd> |
| Synonym for <a class="link" href="#def_object_name">object name</a>. |
| </dd><dt><span class="term"> |
| <a name="def_object_name"></a>object name |
| </span></dt><dd> |
| The unique identifier of an <a class="link" href="#def_object">object</a>. The |
| object name is usually represented by a 40 character |
| hexadecimal string. Also colloquially called <a class="link" href="#def_SHA1">SHA-1</a>. |
| </dd><dt><span class="term"> |
| <a name="def_object_type"></a>object type |
| </span></dt><dd> |
| One of the identifiers "<a class="link" href="#def_commit_object">commit</a>", |
| "<a class="link" href="#def_tree_object">tree</a>", "<a class="link" href="#def_tag_object">tag</a>" or |
| "<a class="link" href="#def_blob_object">blob</a>" describing the type of an |
| <a class="link" href="#def_object">object</a>. |
| </dd><dt><span class="term"> |
| <a name="def_octopus"></a>octopus |
| </span></dt><dd> |
| To <a class="link" href="#def_merge">merge</a> more than two <a class="link" href="#def_branch">branches</a>. |
| </dd><dt><span class="term"> |
| <a name="def_origin"></a>origin |
| </span></dt><dd> |
| The default upstream <a class="link" href="#def_repository">repository</a>. Most projects have |
| at least one upstream project which they track. By default |
| <span class="emphasis"><em>origin</em></span> is used for that purpose. New upstream updates |
| will be fetched into <a class="link" href="#def_remote_tracking_branch">remote-tracking branches</a> named |
| origin/name-of-upstream-branch, which you can see using |
| <code class="literal">git branch -r</code>. |
| </dd><dt><span class="term"> |
| <a name="def_pack"></a>pack |
| </span></dt><dd> |
| A set of objects which have been compressed into one file (to save space |
| or to transmit them efficiently). |
| </dd><dt><span class="term"> |
| <a name="def_pack_index"></a>pack index |
| </span></dt><dd> |
| The list of identifiers, and other information, of the objects in a |
| <a class="link" href="#def_pack">pack</a>, to assist in efficiently accessing the contents of a |
| pack. |
| </dd><dt><span class="term"> |
| <a name="def_pathspec"></a>pathspec |
| </span></dt><dd><p class="simpara"> |
| Pattern used to limit paths in Git commands. |
| </p><p class="simpara">Pathspecs are used on the command line of "git ls-files", "git |
| ls-tree", "git add", "git grep", "git diff", "git checkout", |
| and many other commands to |
| limit the scope of operations to some subset of the tree or |
| worktree. See the documentation of each command for whether |
| paths are relative to the current directory or toplevel. The |
| pathspec syntax is as follows:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| any path matches itself |
| </li><li class="listitem"> |
| the pathspec up to the last slash represents a |
| directory prefix. The scope of that pathspec is |
| limited to that subtree. |
| </li><li class="listitem"> |
| the rest of the pathspec is a pattern for the remainder |
| of the pathname. Paths relative to the directory |
| prefix will be matched against that pattern using fnmatch(3); |
| in particular, <span class="emphasis"><em>*</em></span> and <span class="emphasis"><em>?</em></span> <span class="emphasis"><em>can</em></span> match directory separators. |
| </li></ul></div><p class="simpara">For example, Documentation/*.jpg will match all .jpg files |
| in the Documentation subtree, |
| including Documentation/chapter_1/figure_1.jpg.</p><p class="simpara">A pathspec that begins with a colon <code class="literal">:</code> has special meaning. In the |
| short form, the leading colon <code class="literal">:</code> is followed by zero or more "magic |
| signature" letters (which optionally is terminated by another colon <code class="literal">:</code>), |
| and the remainder is the pattern to match against the path. |
| The "magic signature" consists of ASCII symbols that are neither |
| alphanumeric, glob, regex special characters nor colon. |
| The optional colon that terminates the "magic signature" can be |
| omitted if the pattern begins with a character that does not belong to |
| "magic signature" symbol set and is not a colon.</p><p class="simpara">In the long form, the leading colon <code class="literal">:</code> is followed by an open |
| parenthesis <code class="literal">(</code>, a comma-separated list of zero or more "magic words", |
| and a close parentheses <code class="literal">)</code>, and the remainder is the pattern to match |
| against the path.</p><p class="simpara">A pathspec with only a colon means "there is no pathspec". This form |
| should not be combined with other pathspec.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"> |
| top |
| </span></dt><dd> |
| The magic word <code class="literal">top</code> (magic signature: <code class="literal">/</code>) makes the pattern |
| match from the root of the working tree, even when you are |
| running the command from inside a subdirectory. |
| </dd><dt><span class="term"> |
| literal |
| </span></dt><dd> |
| Wildcards in the pattern such as <code class="literal">*</code> or <code class="literal">?</code> are treated |
| as literal characters. |
| </dd><dt><span class="term"> |
| icase |
| </span></dt><dd> |
| Case insensitive match. |
| </dd><dt><span class="term"> |
| glob |
| </span></dt><dd><p class="simpara"> |
| Git treats the pattern as a shell glob suitable for |
| consumption by fnmatch(3) with the FNM_PATHNAME flag: |
| wildcards in the pattern will not match a / in the pathname. |
| For example, "Documentation/*.html" matches |
| "Documentation/git.html" but not "Documentation/ppc/ppc.html" |
| or "tools/perf/Documentation/perf.html". |
| </p><p class="simpara">Two consecutive asterisks ("<code class="literal">**</code>") in patterns matched against |
| full pathname may have special meaning:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| A leading "<code class="literal">**</code>" followed by a slash means match in all |
| directories. For example, "<code class="literal">**/foo</code>" matches file or directory |
| "<code class="literal">foo</code>" anywhere, the same as pattern "<code class="literal">foo</code>". "<code class="literal">**/foo/bar</code>" |
| matches file or directory "<code class="literal">bar</code>" anywhere that is directly |
| under directory "<code class="literal">foo</code>". |
| </li><li class="listitem"> |
| A trailing "<code class="literal">/**</code>" matches everything inside. For example, |
| "<code class="literal">abc/**</code>" matches all files inside directory "abc", relative |
| to the location of the <code class="literal">.gitignore</code> file, with infinite depth. |
| </li><li class="listitem"> |
| A slash followed by two consecutive asterisks then a slash |
| matches zero or more directories. For example, "<code class="literal">a/**/b</code>" |
| matches "<code class="literal">a/b</code>", "<code class="literal">a/x/b</code>", "<code class="literal">a/x/y/b</code>" and so on. |
| </li><li class="listitem"><p class="simpara"> |
| Other consecutive asterisks are considered invalid. |
| </p><p class="simpara">Glob magic is incompatible with literal magic.</p></li></ul></div></dd><dt><span class="term"> |
| attr |
| </span></dt><dd><p class="simpara"> |
| After <code class="literal">attr:</code> comes a space separated list of "attribute |
| requirements", all of which must be met in order for the |
| path to be considered a match; this is in addition to the |
| usual non-magic pathspec pattern matching. |
| See <a class="ulink" href="gitattributes.html" target="_top">gitattributes(5)</a>. |
| </p><p class="simpara">Each of the attribute requirements for the path takes one of |
| these forms:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| "<code class="literal">ATTR</code>" requires that the attribute <code class="literal">ATTR</code> be set. |
| </li><li class="listitem"> |
| "<code class="literal">-ATTR</code>" requires that the attribute <code class="literal">ATTR</code> be unset. |
| </li><li class="listitem"> |
| "<code class="literal">ATTR=VALUE</code>" requires that the attribute <code class="literal">ATTR</code> be |
| set to the string <code class="literal">VALUE</code>. |
| </li><li class="listitem"><p class="simpara"> |
| "<code class="literal">!ATTR</code>" requires that the attribute <code class="literal">ATTR</code> be |
| unspecified. |
| </p><p class="simpara">Note that when matching against a tree object, attributes are still |
| obtained from working tree, not from the given tree object.</p></li></ul></div></dd><dt><span class="term"> |
| exclude |
| </span></dt><dd> |
| After a path matches any non-exclude pathspec, it will be run |
| through all exclude pathspecs (magic signature: <code class="literal">!</code> or its |
| synonym <code class="literal">^</code>). If it matches, the path is ignored. When there |
| is no non-exclude pathspec, the exclusion is applied to the |
| result set as if invoked without any pathspec. |
| </dd></dl></div></dd><dt><span class="term"> |
| <a name="def_parent"></a>parent |
| </span></dt><dd> |
| A <a class="link" href="#def_commit_object">commit object</a> contains a (possibly empty) list |
| of the logical predecessor(s) in the line of development, i.e. its |
| parents. |
| </dd><dt><span class="term"> |
| <a name="def_pickaxe"></a>pickaxe |
| </span></dt><dd> |
| The term <a class="link" href="#def_pickaxe">pickaxe</a> refers to an option to the diffcore |
| routines that help select changes that add or delete a given text |
| string. With the <code class="literal">--pickaxe-all</code> option, it can be used to view the full |
| <a class="link" href="#def_changeset">changeset</a> that introduced or removed, say, a |
| particular line of text. See <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>. |
| </dd><dt><span class="term"> |
| <a name="def_plumbing"></a>plumbing |
| </span></dt><dd> |
| Cute name for <a class="link" href="#def_core_git">core Git</a>. |
| </dd><dt><span class="term"> |
| <a name="def_porcelain"></a>porcelain |
| </span></dt><dd> |
| Cute name for programs and program suites depending on |
| <a class="link" href="#def_core_git">core Git</a>, presenting a high level access to |
| core Git. Porcelains expose more of a <a class="link" href="#def_SCM">SCM</a> |
| interface than the <a class="link" href="#def_plumbing">plumbing</a>. |
| </dd><dt><span class="term"> |
| <a name="def_per_worktree_ref"></a>per-worktree ref |
| </span></dt><dd> |
| Refs that are per-<a class="link" href="#def_working_tree">worktree</a>, rather than |
| global. This is presently only <a class="link" href="#def_HEAD">HEAD</a> and any refs |
| that start with <code class="literal">refs/bisect/</code>, but might later include other |
| unusual refs. |
| </dd><dt><span class="term"> |
| <a name="def_pseudoref"></a>pseudoref |
| </span></dt><dd> |
| Pseudorefs are a class of files under <code class="literal">$GIT_DIR</code> which behave |
| like refs for the purposes of rev-parse, but which are treated |
| specially by git. Pseudorefs both have names that are all-caps, |
| and always start with a line consisting of a |
| <a class="link" href="#def_SHA1">SHA-1</a> followed by whitespace. So, HEAD is not a |
| pseudoref, because it is sometimes a symbolic ref. They might |
| optionally contain some additional data. <code class="literal">MERGE_HEAD</code> and |
| <code class="literal">CHERRY_PICK_HEAD</code> are examples. Unlike |
| <a class="link" href="#def_per_worktree_ref">per-worktree refs</a>, these files cannot |
| be symbolic refs, and never have reflogs. They also cannot be |
| updated through the normal ref update machinery. Instead, |
| they are updated by directly writing to the files. However, |
| they can be read as if they were refs, so <code class="literal">git rev-parse |
| MERGE_HEAD</code> will work. |
| </dd><dt><span class="term"> |
| <a name="def_pull"></a>pull |
| </span></dt><dd> |
| Pulling a <a class="link" href="#def_branch">branch</a> means to <a class="link" href="#def_fetch">fetch</a> it and |
| <a class="link" href="#def_merge">merge</a> it. See also <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>. |
| </dd><dt><span class="term"> |
| <a name="def_push"></a>push |
| </span></dt><dd> |
| Pushing a <a class="link" href="#def_branch">branch</a> means to get the branch’s |
| <a class="link" href="#def_head_ref">head ref</a> from a remote <a class="link" href="#def_repository">repository</a>, |
| find out if it is an ancestor to the branch’s local |
| head ref, and in that case, putting all |
| objects, which are <a class="link" href="#def_reachable">reachable</a> from the local |
| head ref, and which are missing from the remote |
| repository, into the remote |
| <a class="link" href="#def_object_database">object database</a>, and updating the remote |
| head ref. If the remote <a class="link" href="#def_head">head</a> is not an |
| ancestor to the local head, the push fails. |
| </dd><dt><span class="term"> |
| <a name="def_reachable"></a>reachable |
| </span></dt><dd> |
| All of the ancestors of a given <a class="link" href="#def_commit">commit</a> are said to be |
| "reachable" from that commit. More |
| generally, one <a class="link" href="#def_object">object</a> is reachable from |
| another if we can reach the one from the other by a <a class="link" href="#def_chain">chain</a> |
| that follows <a class="link" href="#def_tag">tags</a> to whatever they tag, |
| <a class="link" href="#def_commit_object">commits</a> to their parents or trees, and |
| <a class="link" href="#def_tree_object">trees</a> to the trees or <a class="link" href="#def_blob_object">blobs</a> |
| that they contain. |
| </dd><dt><span class="term"> |
| <a name="def_rebase"></a>rebase |
| </span></dt><dd> |
| To reapply a series of changes from a <a class="link" href="#def_branch">branch</a> to a |
| different base, and reset the <a class="link" href="#def_head">head</a> of that branch |
| to the result. |
| </dd><dt><span class="term"> |
| <a name="def_ref"></a>ref |
| </span></dt><dd><p class="simpara"> |
| A name that begins with <code class="literal">refs/</code> (e.g. <code class="literal">refs/heads/master</code>) |
| that points to an <a class="link" href="#def_object_name">object name</a> or another |
| ref (the latter is called a <a class="link" href="#def_symref">symbolic ref</a>). |
| For convenience, a ref can sometimes be abbreviated when used |
| as an argument to a Git command; see <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> |
| for details. |
| Refs are stored in the <a class="link" href="#def_repository">repository</a>. |
| </p><p class="simpara">The ref namespace is hierarchical. |
| Different subhierarchies are used for different purposes (e.g. the |
| <code class="literal">refs/heads/</code> hierarchy is used to represent local branches).</p><p class="simpara">There are a few special-purpose refs that do not begin with <code class="literal">refs/</code>. |
| The most notable example is <code class="literal">HEAD</code>.</p></dd><dt><span class="term"> |
| <a name="def_reflog"></a>reflog |
| </span></dt><dd> |
| A reflog shows the local "history" of a ref. In other words, |
| it can tell you what the 3rd last revision in <span class="emphasis"><em>this</em></span> repository |
| was, and what was the current state in <span class="emphasis"><em>this</em></span> repository, |
| yesterday 9:14pm. See <a class="ulink" href="git-reflog.html" target="_top">git-reflog(1)</a> for details. |
| </dd><dt><span class="term"> |
| <a name="def_refspec"></a>refspec |
| </span></dt><dd> |
| A "refspec" is used by <a class="link" href="#def_fetch">fetch</a> and |
| <a class="link" href="#def_push">push</a> to describe the mapping between remote |
| <a class="link" href="#def_ref">ref</a> and local ref. |
| </dd><dt><span class="term"> |
| <a name="def_remote"></a>remote repository |
| </span></dt><dd> |
| A <a class="link" href="#def_repository">repository</a> which is used to track the same |
| project but resides somewhere else. To communicate with remotes, |
| see <a class="link" href="#def_fetch">fetch</a> or <a class="link" href="#def_push">push</a>. |
| </dd><dt><span class="term"> |
| <a name="def_remote_tracking_branch"></a>remote-tracking branch |
| </span></dt><dd> |
| A <a class="link" href="#def_ref">ref</a> that is used to follow changes from another |
| <a class="link" href="#def_repository">repository</a>. It typically looks like |
| <span class="emphasis"><em>refs/remotes/foo/bar</em></span> (indicating that it tracks a branch named |
| <span class="emphasis"><em>bar</em></span> in a remote named <span class="emphasis"><em>foo</em></span>), and matches the right-hand-side of |
| a configured fetch <a class="link" href="#def_refspec">refspec</a>. A remote-tracking |
| branch should not contain direct modifications or have local |
| commits made to it. |
| </dd><dt><span class="term"> |
| <a name="def_repository"></a>repository |
| </span></dt><dd> |
| A collection of <a class="link" href="#def_ref">refs</a> together with an |
| <a class="link" href="#def_object_database">object database</a> containing all objects |
| which are <a class="link" href="#def_reachable">reachable</a> from the refs, possibly |
| accompanied by meta data from one or more <a class="link" href="#def_porcelain">porcelains</a>. A |
| repository can share an object database with other repositories |
| via <a class="link" href="#def_alternate_object_database">alternates mechanism</a>. |
| </dd><dt><span class="term"> |
| <a name="def_resolve"></a>resolve |
| </span></dt><dd> |
| The action of fixing up manually what a failed automatic |
| <a class="link" href="#def_merge">merge</a> left behind. |
| </dd><dt><span class="term"> |
| <a name="def_revision"></a>revision |
| </span></dt><dd> |
| Synonym for <a class="link" href="#def_commit">commit</a> (the noun). |
| </dd><dt><span class="term"> |
| <a name="def_rewind"></a>rewind |
| </span></dt><dd> |
| To throw away part of the development, i.e. to assign the |
| <a class="link" href="#def_head">head</a> to an earlier <a class="link" href="#def_revision">revision</a>. |
| </dd><dt><span class="term"> |
| <a name="def_SCM"></a>SCM |
| </span></dt><dd> |
| Source code management (tool). |
| </dd><dt><span class="term"> |
| <a name="def_SHA1"></a>SHA-1 |
| </span></dt><dd> |
| "Secure Hash Algorithm 1"; a cryptographic hash function. |
| In the context of Git used as a synonym for <a class="link" href="#def_object_name">object name</a>. |
| </dd><dt><span class="term"> |
| <a name="def_shallow_clone"></a>shallow clone |
| </span></dt><dd> |
| Mostly a synonym to <a class="link" href="#def_shallow_repository">shallow repository</a> |
| but the phrase makes it more explicit that it was created by |
| running <code class="literal">git clone --depth=...</code> command. |
| </dd><dt><span class="term"> |
| <a name="def_shallow_repository"></a>shallow repository |
| </span></dt><dd> |
| A shallow <a class="link" href="#def_repository">repository</a> has an incomplete |
| history some of whose <a class="link" href="#def_commit">commits</a> have <a class="link" href="#def_parent">parents</a> cauterized away (in other |
| words, Git is told to pretend that these commits do not have the |
| parents, even though they are recorded in the <a class="link" href="#def_commit_object">commit object</a>). This is sometimes useful when you are interested only in the |
| recent history of a project even though the real history recorded in the |
| upstream is much larger. A shallow repository |
| is created by giving the <code class="literal">--depth</code> option to <a class="ulink" href="git-clone.html" target="_top">git-clone(1)</a>, and |
| its history can be later deepened with <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>. |
| </dd><dt><span class="term"> |
| <a name="def_stash"></a>stash entry |
| </span></dt><dd> |
| An <a class="link" href="#def_object">object</a> used to temporarily store the contents of a |
| <a class="link" href="#def_dirty">dirty</a> working directory and the index for future reuse. |
| </dd><dt><span class="term"> |
| <a name="def_submodule"></a>submodule |
| </span></dt><dd> |
| A <a class="link" href="#def_repository">repository</a> that holds the history of a |
| separate project inside another repository (the latter of |
| which is called <a class="link" href="#def_superproject">superproject</a>). |
| </dd><dt><span class="term"> |
| <a name="def_superproject"></a>superproject |
| </span></dt><dd> |
| A <a class="link" href="#def_repository">repository</a> that references repositories |
| of other projects in its working tree as <a class="link" href="#def_submodule">submodules</a>. |
| The superproject knows about the names of (but does not hold |
| copies of) commit objects of the contained submodules. |
| </dd><dt><span class="term"> |
| <a name="def_symref"></a>symref |
| </span></dt><dd> |
| Symbolic reference: instead of containing the <a class="link" href="#def_SHA1">SHA-1</a> |
| id itself, it is of the format <span class="emphasis"><em>ref: refs/some/thing</em></span> and when |
| referenced, it recursively dereferences to this reference. |
| <span class="emphasis"><em><a class="link" href="#def_HEAD">HEAD</a></em></span> is a prime example of a symref. Symbolic |
| references are manipulated with the <a class="ulink" href="git-symbolic-ref.html" target="_top">git-symbolic-ref(1)</a> |
| command. |
| </dd><dt><span class="term"> |
| <a name="def_tag"></a>tag |
| </span></dt><dd> |
| A <a class="link" href="#def_ref">ref</a> under <code class="literal">refs/tags/</code> namespace that points to an |
| object of an arbitrary type (typically a tag points to either a |
| <a class="link" href="#def_tag_object">tag</a> or a <a class="link" href="#def_commit_object">commit object</a>). |
| In contrast to a <a class="link" href="#def_head">head</a>, a tag is not updated by |
| the <code class="literal">commit</code> command. A Git tag has nothing to do with a Lisp |
| tag (which would be called an <a class="link" href="#def_object_type">object type</a> |
| in Git’s context). A tag is most typically used to mark a particular |
| point in the commit ancestry <a class="link" href="#def_chain">chain</a>. |
| </dd><dt><span class="term"> |
| <a name="def_tag_object"></a>tag object |
| </span></dt><dd> |
| An <a class="link" href="#def_object">object</a> containing a <a class="link" href="#def_ref">ref</a> pointing to |
| another object, which can contain a message just like a |
| <a class="link" href="#def_commit_object">commit object</a>. It can also contain a (PGP) |
| signature, in which case it is called a "signed tag object". |
| </dd><dt><span class="term"> |
| <a name="def_topic_branch"></a>topic branch |
| </span></dt><dd> |
| A regular Git <a class="link" href="#def_branch">branch</a> that is used by a developer to |
| identify a conceptual line of development. Since branches are very easy |
| and inexpensive, it is often desirable to have several small branches |
| that each contain very well defined concepts or small incremental yet |
| related changes. |
| </dd><dt><span class="term"> |
| <a name="def_tree"></a>tree |
| </span></dt><dd> |
| Either a <a class="link" href="#def_working_tree">working tree</a>, or a <a class="link" href="#def_tree_object">tree object</a> together with the dependent <a class="link" href="#def_blob_object">blob</a> and tree objects |
| (i.e. a stored representation of a working tree). |
| </dd><dt><span class="term"> |
| <a name="def_tree_object"></a>tree object |
| </span></dt><dd> |
| An <a class="link" href="#def_object">object</a> containing a list of file names and modes along |
| with refs to the associated blob and/or tree objects. A |
| <a class="link" href="#def_tree">tree</a> is equivalent to a <a class="link" href="#def_directory">directory</a>. |
| </dd><dt><span class="term"> |
| <a name="def_tree-ish"></a>tree-ish (also treeish) |
| </span></dt><dd> |
| A <a class="link" href="#def_tree_object">tree object</a> or an <a class="link" href="#def_object">object</a> |
| that can be recursively dereferenced to a tree object. |
| Dereferencing a <a class="link" href="#def_commit_object">commit object</a> yields the |
| tree object corresponding to the <a class="link" href="#def_revision">revision</a>'s |
| top <a class="link" href="#def_directory">directory</a>. |
| The following are all tree-ishes: |
| a <a class="link" href="#def_commit-ish">commit-ish</a>, |
| a tree object, |
| a <a class="link" href="#def_tag_object">tag object</a> that points to a tree object, |
| a tag object that points to a tag object that points to a tree |
| object, |
| etc. |
| </dd><dt><span class="term"> |
| <a name="def_unmerged_index"></a>unmerged index |
| </span></dt><dd> |
| An <a class="link" href="#def_index">index</a> which contains unmerged |
| <a class="link" href="#def_index_entry">index entries</a>. |
| </dd><dt><span class="term"> |
| <a name="def_unreachable_object"></a>unreachable object |
| </span></dt><dd> |
| An <a class="link" href="#def_object">object</a> which is not <a class="link" href="#def_reachable">reachable</a> from a |
| <a class="link" href="#def_branch">branch</a>, <a class="link" href="#def_tag">tag</a>, or any other reference. |
| </dd><dt><span class="term"> |
| <a name="def_upstream_branch"></a>upstream branch |
| </span></dt><dd> |
| The default <a class="link" href="#def_branch">branch</a> that is merged into the branch in |
| question (or the branch in question is rebased onto). It is configured |
| via branch.<name>.remote and branch.<name>.merge. If the upstream branch |
| of <span class="emphasis"><em>A</em></span> is <span class="emphasis"><em>origin/B</em></span> sometimes we say "<span class="emphasis"><em>A</em></span> is tracking <span class="emphasis"><em>origin/B</em></span>". |
| </dd><dt><span class="term"> |
| <a name="def_working_tree"></a>working tree |
| </span></dt><dd> |
| The tree of actual checked out files. The working tree normally |
| contains the contents of the <a class="link" href="#def_HEAD">HEAD</a> commit’s tree, |
| plus any local changes that you have made but not yet committed. |
| </dd></dl></div></div></div><div class="appendix"><div class="titlepage"><div><div><h1 class="title"><a name="git-quick-start"></a>Appendix A. Git Quick Reference</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#quick-creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#managing-branches">Managing branches</a></span></dt><dt><span class="section"><a href="#exploring-history">Exploring history</a></span></dt><dt><span class="section"><a href="#making-changes">Making changes</a></span></dt><dt><span class="section"><a href="#merging">Merging</a></span></dt><dt><span class="section"><a href="#sharing-your-changes">Sharing your changes</a></span></dt><dt><span class="section"><a href="#repository-maintenance">Repository maintenance</a></span></dt></dl></div><p>This is a quick summary of the major commands; the previous chapters |
| explain how these work in more detail.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="quick-creating-a-new-repository"></a>Creating a new repository</h2></div></div></div><p>From a tarball:</p><pre class="literallayout">$ tar xzf project.tar.gz |
| $ cd project |
| $ git init |
| Initialized empty Git repository in .git/ |
| $ git add . |
| $ git commit</pre><p>From a remote repository:</p><pre class="literallayout">$ git clone git://example.com/pub/project.git |
| $ cd project</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="managing-branches"></a>Managing branches</h2></div></div></div><pre class="literallayout">$ git branch # list all local branches in this repo |
| $ git checkout test # switch working directory to branch "test" |
| $ git branch new # create branch "new" starting at current HEAD |
| $ git branch -d new # delete branch "new"</pre><p>Instead of basing a new branch on current HEAD (the default), use:</p><pre class="literallayout">$ git branch new test # branch named "test" |
| $ git branch new v2.6.15 # tag named v2.6.15 |
| $ git branch new HEAD^ # commit before the most recent |
| $ git branch new HEAD^^ # commit before that |
| $ git branch new test~10 # ten commits before tip of branch "test"</pre><p>Create and switch to a new branch at the same time:</p><pre class="literallayout">$ git checkout -b new v2.6.15</pre><p>Update and examine branches from the repository you cloned from:</p><pre class="literallayout">$ git fetch # update |
| $ git branch -r # list |
| origin/master |
| origin/next |
| ... |
| $ git checkout -b masterwork origin/master</pre><p>Fetch a branch from a different repository, and give it a new |
| name in your repository:</p><pre class="literallayout">$ git fetch git://example.com/project.git theirbranch:mybranch |
| $ git fetch git://example.com/project.git v2.6.15:mybranch</pre><p>Keep a list of repositories you work with regularly:</p><pre class="literallayout">$ git remote add example git://example.com/project.git |
| $ git remote # list remote repositories |
| example |
| origin |
| $ git remote show example # get details |
| * remote example |
| URL: git://example.com/project.git |
| Tracked remote branches |
| master |
| next |
| ... |
| $ git fetch example # update branches from example |
| $ git branch -r # list all remote branches</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="exploring-history"></a>Exploring history</h2></div></div></div><pre class="literallayout">$ gitk # visualize and browse history |
| $ git log # list all commits |
| $ git log src/ # ...modifying src/ |
| $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15 |
| $ git log master..test # ...in branch test, not in branch master |
| $ git log test..master # ...in branch master, but not in test |
| $ git log test...master # ...in one branch, not in both |
| $ git log -S'foo()' # ...where difference contain "foo()" |
| $ git log --since="2 weeks ago" |
| $ git log -p # show patches as well |
| $ git show # most recent commit |
| $ git diff v2.6.15..v2.6.16 # diff between two tagged versions |
| $ git diff v2.6.15..HEAD # diff with current head |
| $ git grep "foo()" # search working directory for "foo()" |
| $ git grep v2.6.15 "foo()" # search old tree for "foo()" |
| $ git show v2.6.15:a.txt # look at old version of a.txt</pre><p>Search for regressions:</p><pre class="literallayout">$ git bisect start |
| $ git bisect bad # current version is bad |
| $ git bisect good v2.6.13-rc2 # last known good revision |
| Bisecting: 675 revisions left to test after this |
| # test here, then: |
| $ git bisect good # if this revision is good, or |
| $ git bisect bad # if this revision is bad. |
| # repeat until done.</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="making-changes"></a>Making changes</h2></div></div></div><p>Make sure Git knows who to blame:</p><pre class="literallayout">$ cat >>~/.gitconfig <<\EOF |
| [user] |
| name = Your Name Comes Here |
| email = you@yourdomain.example.com |
| EOF</pre><p>Select file contents to include in the next commit, then make the |
| commit:</p><pre class="literallayout">$ git add a.txt # updated file |
| $ git add b.txt # new file |
| $ git rm c.txt # old file |
| $ git commit</pre><p>Or, prepare and create the commit in one step:</p><pre class="literallayout">$ git commit d.txt # use latest content only of d.txt |
| $ git commit -a # use latest content of all tracked files</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging"></a>Merging</h2></div></div></div><pre class="literallayout">$ git merge test # merge branch "test" into the current branch |
| $ git pull git://example.com/project.git master |
| # fetch and merge in remote branch |
| $ git pull . test # equivalent to git merge test</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sharing-your-changes"></a>Sharing your changes</h2></div></div></div><p>Importing or exporting patches:</p><pre class="literallayout">$ git format-patch origin..HEAD # format a patch for each commit |
| # in HEAD but not in origin |
| $ git am mbox # import patches from the mailbox "mbox"</pre><p>Fetch a branch in a different Git repository, then merge into the |
| current branch:</p><pre class="literallayout">$ git pull git://example.com/project.git theirbranch</pre><p>Store the fetched branch into a local branch before merging into the |
| current branch:</p><pre class="literallayout">$ git pull git://example.com/project.git theirbranch:mybranch</pre><p>After creating commits on a local branch, update the remote |
| branch with your commits:</p><pre class="literallayout">$ git push ssh://example.com/project.git mybranch:theirbranch</pre><p>When remote and local branch are both named "test":</p><pre class="literallayout">$ git push ssh://example.com/project.git test</pre><p>Shortcut version for a frequently used remote repository:</p><pre class="literallayout">$ git remote add example ssh://example.com/project.git |
| $ git push example test</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="repository-maintenance"></a>Repository maintenance</h2></div></div></div><p>Check for corruption:</p><pre class="literallayout">$ git fsck</pre><p>Recompress, remove unused cruft:</p><pre class="literallayout">$ git gc</pre></div></div><div class="appendix"><div class="titlepage"><div><div><h1 class="title"><a name="todo"></a>Appendix B. Notes and todo list for this manual</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#todo-list">Todo list</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="todo-list"></a>Todo list</h2></div></div></div><p>This is a work in progress.</p><p>The basic requirements:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| It must be readable in order, from beginning to end, by someone |
| intelligent with a basic grasp of the UNIX command line, but without |
| any special knowledge of Git. If necessary, any other prerequisites |
| should be specifically mentioned as they arise. |
| </li><li class="listitem"> |
| Whenever possible, section headings should clearly describe the task |
| they explain how to do, in language that requires no more knowledge |
| than necessary: for example, "importing patches into a project" rather |
| than "the <code class="literal">git am</code> command" |
| </li></ul></div><p>Think about how to create a clear chapter dependency graph that will |
| allow people to get to important topics without necessarily reading |
| everything in between.</p><p>Scan <code class="literal">Documentation/</code> for other stuff left out; in particular:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| howto’s |
| </li><li class="listitem"> |
| some of <code class="literal">technical/</code>? |
| </li><li class="listitem"> |
| hooks |
| </li><li class="listitem"> |
| list of commands in <a class="ulink" href="git.html" target="_top">git(1)</a> |
| </li></ul></div><p>Scan email archives for other stuff left out</p><p>Scan man pages to see if any assume more background than this manual |
| provides.</p><p>Add more good examples. Entire sections of just cookbook examples |
| might be a good idea; maybe make an "advanced examples" section a |
| standard end-of-chapter section?</p><p>Include cross-references to the glossary, where appropriate.</p><p>Add a section on working with other version control systems, including |
| CVS, Subversion, and just imports of series of release tarballs.</p><p>Write a chapter on using plumbing and writing scripts.</p><p>Alternates, clone -reference, etc.</p><p>More on recovery from repository corruption. See: |
| <a class="ulink" href="http://marc.info/?l=git&m=117263864820799&w=2" target="_top">http://marc.info/?l=git&m=117263864820799&w=2</a> |
| <a class="ulink" href="http://marc.info/?l=git&m=117147855503798&w=2" target="_top">http://marc.info/?l=git&m=117147855503798&w=2</a></p></div></div></div></body></html> |
