| '\" t |
| .\" Title: git-update-ref |
| .\" Author: [FIXME: author] [see http://docbook.sf.net/el/author] |
| .\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/> |
| .\" Date: 10/30/2018 |
| .\" Manual: Git Manual |
| .\" Source: Git 2.19.1.708.g4ede3d42df |
| .\" Language: English |
| .\" |
| .TH "GIT\-UPDATE\-REF" "1" "10/30/2018" "Git 2\&.19\&.1\&.708\&.g4ede3d" "Git Manual" |
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| .\" * MAIN CONTENT STARTS HERE * |
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| .SH "NAME" |
| git-update-ref \- Update the object name stored in a ref safely |
| .SH "SYNOPSIS" |
| .sp |
| .nf |
| \fIgit update\-ref\fR [\-m <reason>] [\-\-no\-deref] (\-d <ref> [<oldvalue>] | [\-\-create\-reflog] <ref> <newvalue> [<oldvalue>] | \-\-stdin [\-z]) |
| .fi |
| .sp |
| .SH "DESCRIPTION" |
| .sp |
| Given two arguments, stores the <newvalue> in the <ref>, possibly dereferencing the symbolic refs\&. E\&.g\&. \fBgit update\-ref HEAD <newvalue>\fR updates the current branch head to the new object\&. |
| .sp |
| Given three arguments, stores the <newvalue> in the <ref>, possibly dereferencing the symbolic refs, after verifying that the current value of the <ref> matches <oldvalue>\&. E\&.g\&. \fBgit update\-ref refs/heads/master <newvalue> <oldvalue>\fR updates the master branch head to <newvalue> only if its current value is <oldvalue>\&. You can specify 40 "0" or an empty string as <oldvalue> to make sure that the ref you are creating does not exist\&. |
| .sp |
| It also allows a "ref" file to be a symbolic pointer to another ref file by starting with the four\-byte header sequence of "ref:"\&. |
| .sp |
| More importantly, it allows the update of a ref file to follow these symbolic pointers, whether they are symlinks or these "regular file symbolic refs"\&. It follows \fBreal\fR symlinks only if they start with "refs/": otherwise it will just try to read them and update them as a regular file (i\&.e\&. it will allow the filesystem to follow them, but will overwrite such a symlink to somewhere else with a regular filename)\&. |
| .sp |
| If \-\-no\-deref is given, <ref> itself is overwritten, rather than the result of following the symbolic pointers\&. |
| .sp |
| In general, using |
| .sp |
| .if n \{\ |
| .RS 4 |
| .\} |
| .nf |
| git update\-ref HEAD "$head" |
| .fi |
| .if n \{\ |
| .RE |
| .\} |
| .sp |
| should be a \fIlot\fR safer than doing |
| .sp |
| .if n \{\ |
| .RS 4 |
| .\} |
| .nf |
| echo "$head" > "$GIT_DIR/HEAD" |
| .fi |
| .if n \{\ |
| .RE |
| .\} |
| .sp |
| both from a symlink following standpoint \fBand\fR an error checking standpoint\&. The "refs/" rule for symlinks means that symlinks that point to "outside" the tree are safe: they\(cqll be followed for reading but not for writing (so we\(cqll never write through a ref symlink to some other tree, if you have copied a whole archive by creating a symlink tree)\&. |
| .sp |
| With \fB\-d\fR flag, it deletes the named <ref> after verifying it still contains <oldvalue>\&. |
| .sp |
| With \fB\-\-stdin\fR, update\-ref reads instructions from standard input and performs all modifications together\&. Specify commands of the form: |
| .sp |
| .if n \{\ |
| .RS 4 |
| .\} |
| .nf |
| update SP <ref> SP <newvalue> [SP <oldvalue>] LF |
| create SP <ref> SP <newvalue> LF |
| delete SP <ref> [SP <oldvalue>] LF |
| verify SP <ref> [SP <oldvalue>] LF |
| option SP <opt> LF |
| .fi |
| .if n \{\ |
| .RE |
| .\} |
| .sp |
| With \fB\-\-create\-reflog\fR, update\-ref will create a reflog for each ref even if one would not ordinarily be created\&. |
| .sp |
| Quote fields containing whitespace as if they were strings in C source code; i\&.e\&., surrounded by double\-quotes and with backslash escapes\&. Use 40 "0" characters or the empty string to specify a zero value\&. To specify a missing value, omit the value and its preceding SP entirely\&. |
| .sp |
| Alternatively, use \fB\-z\fR to specify in NUL\-terminated format, without quoting: |
| .sp |
| .if n \{\ |
| .RS 4 |
| .\} |
| .nf |
| update SP <ref> NUL <newvalue> NUL [<oldvalue>] NUL |
| create SP <ref> NUL <newvalue> NUL |
| delete SP <ref> NUL [<oldvalue>] NUL |
| verify SP <ref> NUL [<oldvalue>] NUL |
| option SP <opt> NUL |
| .fi |
| .if n \{\ |
| .RE |
| .\} |
| .sp |
| In this format, use 40 "0" to specify a zero value, and use the empty string to specify a missing value\&. |
| .sp |
| In either format, values can be specified in any form that Git recognizes as an object name\&. Commands in any other format or a repeated <ref> produce an error\&. Command meanings are: |
| .PP |
| update |
| .RS 4 |
| Set <ref> to <newvalue> after verifying <oldvalue>, if given\&. Specify a zero <newvalue> to ensure the ref does not exist after the update and/or a zero <oldvalue> to make sure the ref does not exist before the update\&. |
| .RE |
| .PP |
| create |
| .RS 4 |
| Create <ref> with <newvalue> after verifying it does not exist\&. The given <newvalue> may not be zero\&. |
| .RE |
| .PP |
| delete |
| .RS 4 |
| Delete <ref> after verifying it exists with <oldvalue>, if given\&. If given, <oldvalue> may not be zero\&. |
| .RE |
| .PP |
| verify |
| .RS 4 |
| Verify <ref> against <oldvalue> but do not change it\&. If <oldvalue> zero or missing, the ref must not exist\&. |
| .RE |
| .PP |
| option |
| .RS 4 |
| Modify behavior of the next command naming a <ref>\&. The only valid option is |
| \fBno\-deref\fR |
| to avoid dereferencing a symbolic ref\&. |
| .RE |
| .sp |
| If all <ref>s can be locked with matching <oldvalue>s simultaneously, all modifications are performed\&. Otherwise, no modifications are performed\&. Note that while each individual <ref> is updated or deleted atomically, a concurrent reader may still see a subset of the modifications\&. |
| .SH "LOGGING UPDATES" |
| .sp |
| If config parameter "core\&.logAllRefUpdates" is true and the ref is one under "refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic ref HEAD; or the file "$GIT_DIR/logs/<ref>" exists then \fBgit update\-ref\fR will append a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all symbolic refs before creating the log name) describing the change in ref value\&. Log lines are formatted as: |
| .sp |
| .if n \{\ |
| .RS 4 |
| .\} |
| .nf |
| oldsha1 SP newsha1 SP committer LF |
| .fi |
| .if n \{\ |
| .RE |
| .\} |
| .sp |
| Where "oldsha1" is the 40 character hexadecimal value previously stored in <ref>, "newsha1" is the 40 character hexadecimal value of <newvalue> and "committer" is the committer\(cqs name, email address and date in the standard Git committer ident format\&. |
| .sp |
| Optionally with \-m: |
| .sp |
| .if n \{\ |
| .RS 4 |
| .\} |
| .nf |
| oldsha1 SP newsha1 SP committer TAB message LF |
| .fi |
| .if n \{\ |
| .RE |
| .\} |
| .sp |
| Where all fields are as described above and "message" is the value supplied to the \-m option\&. |
| .sp |
| An update will fail (without changing <ref>) if the current user is unable to create a new log file, append to the existing log file or does not have committer information available\&. |
| .SH "GIT" |
| .sp |
| Part of the \fBgit\fR(1) suite |