'\" t
.\"     Title: git-update-ref
.\"    Author: [FIXME: author] [see http://www.docbook.org/tdg5/en/html/author]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 2025-06-15
.\"    Manual: Git Manual
.\"    Source: Git 2.50.0
.\"  Language: English
.\"
.TH "GIT\-UPDATE\-REF" "1" "2025\-06\-15" "Git 2\&.50\&.0" "Git Manual"
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.SH "NAME"
git-update-ref \- Update the object name stored in a ref safely
.SH "SYNOPSIS"
.sp
.nf
\fBgit\fR \fBupdate\-ref\fR [\fB\-m\fR \fI<reason>\fR] [\fB\-\-no\-deref\fR] \fB\-d\fR \fI<ref>\fR [\fI<old\-oid>\fR]
\fBgit\fR \fBupdate\-ref\fR [\fB\-m\fR \fI<reason>\fR] [\fB\-\-no\-deref\fR] [\fB\-\-create\-reflog\fR] \fI<ref>\fR \fI<new\-oid>\fR [\fI<old\-oid>\fR]
\fBgit\fR \fBupdate\-ref\fR [\fB\-m\fR \fI<reason>\fR] [\fB\-\-no\-deref\fR] \fB\-\-stdin\fR [\fB\-z\fR] [\fB\-\-batch\-updates\fR]
.fi
.sp
.SH "DESCRIPTION"
.sp
Given two arguments, stores the <new\-oid> in the <ref>, possibly dereferencing the symbolic refs\&. E\&.g\&. \fBgit\fR \fBupdate\-ref\fR \fBHEAD\fR \fI<new\-oid>\fR updates the current branch head to the new object\&.
.sp
Given three arguments, stores the <new\-oid> in the <ref>, possibly dereferencing the symbolic refs, after verifying that the current value of the <ref> matches <old\-oid>\&. E\&.g\&. \fBgit\fR \fBupdate\-ref\fR \fBrefs/heads/master\fR \fI<new\-oid>\fR \fI<old\-oid>\fR updates the master branch head to <new\-oid> only if its current value is <old\-oid>\&. You can specify 40 "0" or an empty string as <old\-oid> to make sure that the ref you are creating does not exist\&.
.sp
The final arguments are object names; this command without any options does not support updating a symbolic ref to point to another ref (see \fBgit-symbolic-ref\fR(1))\&. But \fBgit\fR \fBupdate\-ref\fR \fB\-\-stdin\fR does have the \fBsymref\-*\fR commands so that regular refs and symbolic refs can be committed in the same transaction\&.
.sp
If \-\-no\-deref is given, <ref> itself is overwritten, rather than the result of following the symbolic pointers\&.
.sp
With \fB\-d\fR, it deletes the named <ref> after verifying that it still contains <old\-oid>\&.
.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 <new\-oid> [SP <old\-oid>] LF
create SP <ref> SP <new\-oid> LF
delete SP <ref> [SP <old\-oid>] LF
verify SP <ref> [SP <old\-oid>] LF
symref\-update SP <ref> SP <new\-target> [SP (ref SP <old\-target> | oid SP <old\-oid>)] LF
symref\-create SP <ref> SP <new\-target> LF
symref\-delete SP <ref> [SP <old\-target>] LF
symref\-verify SP <ref> [SP <old\-target>] LF
option SP <opt> LF
start LF
prepare LF
commit LF
abort 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
With \fB\-\-batch\-updates\fR, update\-ref executes the updates in a batch but allows individual updates to fail due to invalid or incorrect user input, applying only the successful updates\&. However, system\-related errors\(emsuch as I/O failures or memory issues\(emwill result in a full failure of all batched updates\&. Any failed updates will be reported in the following format:
.sp
.if n \{\
.RS 4
.\}
.nf
rejected SP (<old\-oid> | <old\-target>) SP (<new\-oid> | <new\-target>) SP <rejection\-reason> LF
.fi
.if n \{\
.RE
.\}
.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 <new\-oid> NUL [<old\-oid>] NUL
create SP <ref> NUL <new\-oid> NUL
delete SP <ref> NUL [<old\-oid>] NUL
verify SP <ref> NUL [<old\-oid>] NUL
symref\-update SP <ref> NUL <new\-target> [NUL (ref NUL <old\-target> | oid NUL <old\-oid>)] NUL
symref\-create SP <ref> NUL <new\-target> NUL
symref\-delete SP <ref> [NUL <old\-target>] NUL
symref\-verify SP <ref> [NUL <old\-target>] NUL
option SP <opt> NUL
start NUL
prepare NUL
commit NUL
abort 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 <new\-oid> after verifying <old\-oid>, if given\&. Specify a zero <new\-oid> to ensure the ref does not exist after the update and/or a zero <old\-oid> to make sure the ref does not exist before the update\&.
.RE
.PP
create
.RS 4
Create <ref> with <new\-oid> after verifying that it does not exist\&. The given <new\-oid> may not be zero\&.
.RE
.PP
delete
.RS 4
Delete <ref> after verifying that it exists with <old\-oid>, if given\&. If given, <old\-oid> may not be zero\&.
.RE
.PP
symref\-update
.RS 4
Set <ref> to <new\-target> after verifying <old\-target> or <old\-oid>, if given\&. Specify a zero <old\-oid> to ensure that the ref does not exist before the update\&.
.RE
.PP
verify
.RS 4
Verify <ref> against <old\-oid> but do not change it\&. If <old\-oid> is zero or missing, the ref must not exist\&.
.RE
.sp
symref\-create: Create symbolic ref <ref> with <new\-target> after verifying that it does not exist\&.
.PP
symref\-delete
.RS 4
Delete <ref> after verifying that it exists with <old\-target>, if given\&.
.RE
.PP
symref\-verify
.RS 4
Verify symbolic <ref> against <old\-target> but do not change it\&. If <old\-target> is missing, the ref must not exist\&. Can only be used in
\fBno\-deref\fR
mode\&.
.RE
.PP
option
.RS 4
Modify the behavior of the next command naming a <ref>\&. The only valid option is
\fBno\-deref\fR
to avoid dereferencing a symbolic ref\&.
.RE
.PP
start
.RS 4
Start a transaction\&. In contrast to a non\-transactional session, a transaction will automatically abort if the session ends without an explicit commit\&. This command may create a new empty transaction when the current one has been committed or aborted already\&.
.RE
.PP
prepare
.RS 4
Prepare to commit the transaction\&. This will create lock files for all queued reference updates\&. If one reference could not be locked, the transaction will be aborted\&.
.RE
.PP
commit
.RS 4
Commit all reference updates queued for the transaction, ending the transaction\&.
.RE
.PP
abort
.RS 4
Abort the transaction, releasing all locks if the transaction is in prepared state\&.
.RE
.sp
If all <ref>s can be locked with matching <old\-oid>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 a pseudoref like HEAD or ORIG_HEAD; or the file "$GIT_DIR/logs/<ref>" exists then \fBgit\fR \fBupdate\-ref\fR will append a line to the log file "$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 <new\-oid> 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 "NOTES"
.sp
Symbolic refs were initially implemented using symbolic links\&. This is now deprecated since not all filesystems support symbolic links\&.
.sp
This command 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)\&.
.SH "SEE ALSO"
.sp
\fBgit-symbolic-ref\fR(1)
.SH "GIT"
.sp
Part of the \fBgit\fR(1) suite