1 <?xml version="1.0" encoding="UTF-8"?>
\r
2 <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
\r
4 <article lang="en" id="git-update-ref(1)">
\r
6 <title>git-update-ref(1)</title>
\r
8 <primary>git-update-ref(1)</primary>
\r
11 <simplesect id="_name">
\r
13 <simpara>git-update-ref - Update the object name stored in a ref safely</simpara>
\r
15 <simplesect id="_synopsis">
\r
16 <title>SYNOPSIS</title>
\r
17 <simpara><emphasis>git update-ref</emphasis> [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>])</simpara>
\r
19 <simplesect id="_description">
\r
20 <title>DESCRIPTION</title>
\r
21 <simpara>Given two arguments, stores the <newvalue> in the <ref>, possibly
\r
22 dereferencing the symbolic refs. E.g. <literal>git update-ref HEAD
\r
23 <newvalue></literal> updates the current branch head to the new object.</simpara>
\r
24 <simpara>Given three arguments, stores the <newvalue> in the <ref>,
\r
25 possibly dereferencing the symbolic refs, after verifying that
\r
26 the current value of the <ref> matches <oldvalue>.
\r
27 E.g. <literal>git update-ref refs/heads/master <newvalue> <oldvalue></literal>
\r
28 updates the master branch head to <newvalue> only if its current
\r
29 value is <oldvalue>. You can specify 40 "0" or an empty string
\r
30 as <oldvalue> to make sure that the ref you are creating does
\r
31 not exist.</simpara>
\r
32 <simpara>It also allows a "ref" file to be a symbolic pointer to another
\r
33 ref file by starting with the four-byte header sequence of
\r
35 <simpara>More importantly, it allows the update of a ref file to follow
\r
36 these symbolic pointers, whether they are symlinks or these
\r
37 "regular file symbolic refs". It follows <emphasis role="strong">real</emphasis> symlinks only
\r
38 if they start with "refs/": otherwise it will just try to read
\r
39 them and update them as a regular file (i.e. it will allow the
\r
40 filesystem to follow them, but will overwrite such a symlink to
\r
41 somewhere else with a regular filename).</simpara>
\r
42 <simpara>If --no-deref is given, <ref> itself is overwritten, rather than
\r
43 the result of following the symbolic pointers.</simpara>
\r
44 <simpara>In general, using</simpara>
\r
45 <literallayout class="monospaced">git update-ref HEAD "$head"</literallayout>
\r
46 <simpara>should be a <emphasis>lot</emphasis> safer than doing</simpara>
\r
47 <literallayout class="monospaced">echo "$head" > "$GIT_DIR/HEAD"</literallayout>
\r
48 <simpara>both from a symlink following standpoint <emphasis role="strong">and</emphasis> an error checking
\r
49 standpoint. The "refs/" rule for symlinks means that symlinks
\r
50 that point to "outside" the tree are safe: they’ll be followed
\r
51 for reading but not for writing (so we’ll never write through a
\r
52 ref symlink to some other tree, if you have copied a whole
\r
53 archive by creating a symlink tree).</simpara>
\r
54 <simpara>With <literal>-d</literal> flag, it deletes the named <ref> after verifying it
\r
55 still contains <oldvalue>.</simpara>
\r
57 <simplesect id="_logging_updates">
\r
58 <title>Logging Updates</title>
\r
59 <simpara>If config parameter "core.logAllRefUpdates" is true or the file
\r
60 "$GIT_DIR/logs/<ref>" exists then <literal>git update-ref</literal> will append
\r
61 a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all
\r
62 symbolic refs before creating the log name) describing the change
\r
63 in ref value. Log lines are formatted as:</simpara>
\r
64 <orderedlist numeration="arabic">
\r
67 oldsha1 SP newsha1 SP committer LF
\r
69 <simpara>Where "oldsha1" is the 40 character hexadecimal value previously
\r
70 stored in <ref>, "newsha1" is the 40 character hexadecimal value of
\r
71 <newvalue> and "committer" is the committer’s name, email address
\r
72 and date in the standard GIT committer ident format.</simpara>
\r
75 <simpara>Optionally with -m:</simpara>
\r
76 <orderedlist numeration="arabic">
\r
79 oldsha1 SP newsha1 SP committer TAB message LF
\r
81 <simpara>Where all fields are as described above and "message" is the
\r
82 value supplied to the -m option.</simpara>
\r
85 <simpara>An update will fail (without changing <ref>) if the current user is
\r
86 unable to create a new log file, append to the existing log file
\r
87 or does not have committer information available.</simpara>
\r
89 <simplesect id="_author">
\r
90 <title>Author</title>
\r
91 <simpara>Written by Linus Torvalds <<ulink url="mailto:torvalds@osdl.org">torvalds@osdl.org</ulink>>.</simpara>
\r
93 <simplesect id="_git">
\r
95 <simpara>Part of the <xref linkend="git(1)"/> suite</simpara>
\r