git-history.adoc

git-history(1)
==============

NAME
----
git-history - EXPERIMENTAL: Rewrite history

SYNOPSIS
--------
[synopsis]
git history drop <commit> [--dry-run] [--update-refs=(branches|head)] [--empty=(drop|keep|abort)]
git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]

DESCRIPTION
-----------

Rewrite history by rearranging or modifying specific commits in the
history.

THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOR MAY CHANGE.

This command is related to linkgit:git-rebase[1] in that both commands can be
used to rewrite history. There are a couple of major differences though:

* Most subcommands of linkgit:git-history[1] can work in a bare repository as
  they do not need to touch either the index or the worktree. The `fixup`
  subcommand is an exception to this, as it reads staged changes from the index.
* linkgit:git-history[1] does not execute any linkgit:githooks[5] at the
  current point in time. This may change in the future.
* linkgit:git-history[1] by default updates all branches that are descendants
  of the original commit to point to the rewritten commit.

Overall, linkgit:git-history[1] aims to provide a more opinionated way to modify
your commit history that is simpler to use compared to linkgit:git-rebase[1] in
general.

Use linkgit:git-rebase[1] if you want to reapply a range of commits onto a
different base, or interactive rebases if you want to edit a range of commits
at once.

LIMITATIONS
-----------

This command does not (yet) work with histories that contain merges. You
should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.

Furthermore, the command does not support operations that can result in merge
conflicts. This limitation is by design as history rewrites are not intended to
be stateful operations. The limitation can be lifted once (if) Git learns about
first-class conflicts.

When using `fixup` with `--empty=drop`, dropping the root commit is not yet
supported. Likewise, `drop` cannot remove the root commit or a merge commit.

COMMANDS
--------

The following commands are available to rewrite history in different ways:

`drop <commit>`::
	Remove the specified commit from the history. All descendants of the
	commit are replayed directly onto its parent.
+
The root commit cannot be dropped as that may lead to edge cases where refs
end up with no commits anymore. Merge commits cannot be dropped either; see
LIMITATIONS.
+
If `HEAD` points at a commit that is to be rewritten, the index and working
tree are updated to match the new `HEAD`. The command aborts before any
references are updated in case local modifications would be overwritten.
+
If replaying any descendant would result in a conflict, the command aborts
with an error.

`fixup <commit>`::
	Apply the currently staged changes to the specified commit. This is
	similar in nature to `git commit --fixup=<commit>` followed by `git
	rebase --autosquash <commit>~`. Changes are applied to the target
	commit by performing a three-way merge between the HEAD commit, the
	target commit and the tree generated from staged changes.
+
The commit message and authorship of the target commit are preserved by
default, unless you specify `--reedit-message`.
+
If applying the staged changes would result in a conflict, the command
aborts with an error. All branches that are descendants of the original
commit are updated to point to the rewritten history.

`reword <commit>`::
	Rewrite the commit message of the specified commit. All the other
	details of this commit remain unchanged. This command will spawn an
	editor with the current message of that commit.

`split <commit> [--] [<pathspec>...]`::
	Interactively split up <commit> into two commits by choosing
	hunks introduced by it that will be moved into the new split-out
	commit. These hunks will then be written into a new commit that
	becomes the parent of the previous commit. The original commit
	stays intact, except that its parent will be the newly split-out
	commit.
+
The commit messages of the split-up commits will be asked for by launching
the configured editor. Authorship of the commit will be the same as for the
original commit.
+
If passed, _<pathspec>_ can be used to limit which changes shall be split out
of the original commit. Files not matching any of the pathspecs will remain
part of the original commit. For more details, see the 'pathspec' entry in
linkgit:gitglossary[7].
+
It is invalid to select either all or no hunks, as that would lead to
one of the commits becoming empty.

OPTIONS
-------

`--dry-run`::
	Do not update any references, but instead print any ref updates in a
	format that can be consumed by linkgit:git-update-ref[1]. Necessary new
	objects will be written into the repository, so applying these printed
	ref updates is generally safe.

`--reedit-message`::
	Open an editor to modify the target commit's message.

`--empty=(drop|keep|abort)`::
	Control what happens when a commit becomes empty as a result of the
	fixup. This can happen in two situations:
+
--
* The fixup target itself becomes empty because the staged changes exactly
  cancel out all changes introduced by that commit.

* A descendant commit becomes empty during replay because it introduced the
  same change that was just fixed up into an ancestor.
--
+
With `drop` (the default), empty commits are removed from the rewritten
history. Descendants of a dropped target commit are replayed directly onto
the target's parent. Note that dropping the root commit is not supported;
see LIMITATIONS.
+
With `keep`, empty commits are retained in the rewritten history as-is.
+
With `abort`, the command stops with an error if any commit would become
empty.

`--update-refs=(branches|head)`::
	Control which references will be updated by the command, if any. With
	`branches`, all local branches that point to commits which are
	descendants of the original commit will be rewritten. With `head`, only
	the current `HEAD` reference will be rewritten. Defaults to `branches`.

EXAMPLES
--------

Fixup a commit
~~~~~~~~~~~~~~

----------
$ git log --oneline --stat
abc1234 (HEAD -> main) third
 third.txt | 1 +
def5678 second
 second.txt | 1 +
ghi9012 first
 first.txt | 1 +

$ echo "change" >>unrelated.txt
$ git add unrelated.txt
$ git history fixup ghi9012

$ git log --oneline --stat
jkl3456 (HEAD -> main) third
 third.txt | 1 +
mno7890 second
 second.txt | 1 +
pqr1234 first
 first.txt     | 1 +
 unrelated.txt | 1 +
----------

The staged addition of `unrelated.txt` has been incorporated into the `first`
commit. All descendant commits have been replayed on top of the rewritten
history.

Drop a commit
~~~~~~~~~~~~~

----------
$ git log --oneline
abc1234 (HEAD -> main) third
def5678 second
ghi9012 first

$ git history drop 'main^{/second}'

$ git log --oneline
jkl3456 (HEAD -> main) third
ghi9012 first
----------

The `second` commit has been removed from the history, and `third` has been
replayed directly on top of `first`. All branches that pointed at the dropped
commit have been moved to its parent.

Split a commit
~~~~~~~~~~~~~~

----------
$ git log --stat --oneline
3f81232 (HEAD -> main) original
 bar | 1 +
 foo | 1 +
 2 files changed, 2 insertions(+)

$ git history split HEAD
diff --git a/bar b/bar
new file mode 100644
index 0000000..5716ca5
--- /dev/null
+++ b/bar
@@ -0,0 +1 @@
+bar
(1/1) Stage addition [y,n,q,a,d,p,?]? y

diff --git a/foo b/foo
new file mode 100644
index 0000000..257cc56
--- /dev/null
+++ b/foo
@@ -0,0 +1 @@
+foo
(1/1) Stage addition [y,n,q,a,d,p,?]? n

$ git log --stat --oneline
7cebe64 (HEAD -> main) original
 foo | 1 +
 1 file changed, 1 insertion(+)
d1582f3 split-out commit
 bar | 1 +
 1 file changed, 1 insertion(+)
----------

GIT
---
Part of the linkgit:git[1] suite