man1/git-update-ref.1 - pub/scm/git/git-manpages - Git at Google

 '\" 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: 02/19/2019
 .\"    Manual: Git Manual
 .\"    Source: Git 2.21.0.rc2
 .\"  Language: English
 .\"
 .TH "GIT\-UPDATE\-REF" "1" "02/19/2019" "Git 2\&.21\&.0\&.rc2" "Git Manual"
 .\" -----------------------------------------------------------------
 .\" * Define some portability stuff
 .\" -----------------------------------------------------------------
 .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 .\" http://bugs.debian.org/507673
 .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
 .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 .ie \n(.g .ds Aq \(aq
 .el       .ds Aq '
 .\" -----------------------------------------------------------------
 .\" * set default formatting
 .\" -----------------------------------------------------------------
 .\" disable hyphenation
 .nh
 .\" disable justification (adjust text to left margin only)
 .ad l
 .\" -----------------------------------------------------------------
 .\" * MAIN CONTENT STARTS HERE *
 .\" -----------------------------------------------------------------
 .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
	'\" 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: 02/19/2019
	.\" Manual: Git Manual
	.\" Source: Git 2.21.0.rc2
	.\" Language: English
	.\"
	.TH "GIT\-UPDATE\-REF" "1" "02/19/2019" "Git 2\&.21\&.0\&.rc2" "Git Manual"
	.\" -----------------------------------------------------------------
	.\" * Define some portability stuff
	.\" -----------------------------------------------------------------
	.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	.\" http://bugs.debian.org/507673
	.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
	.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	.ie \n(.g .ds Aq \(aq
	.el .ds Aq '
	.\" -----------------------------------------------------------------
	.\" * set default formatting
	.\" -----------------------------------------------------------------
	.\" disable hyphenation
	.nh
	.\" disable justification (adjust text to left margin only)
	.ad l
	.\" -----------------------------------------------------------------
	.\" * MAIN CONTENT STARTS HERE *
	.\" -----------------------------------------------------------------
	.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