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<body class="manpage">
<div id="header">
<h1>
git-update-ref(1) Manual Page
</h1>
<h2>NAME</h2>
<div class="sectionbody">
<p>git-update-ref -
Update the object name stored in a ref safely
</p>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="verseblock">
<pre class="content"><em>git update-ref</em> [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] [--create-reflog] <ref> <newvalue> [<oldvalue>] | --stdin [-z])</pre>
<div class="attribution">
</div></div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph"><p>Given two arguments, stores the <newvalue> in the <ref>, possibly
dereferencing the symbolic refs. E.g. <code>git update-ref HEAD
<newvalue></code> updates the current branch head to the new object.</p></div>
<div class="paragraph"><p>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. <code>git update-ref refs/heads/master <newvalue> <oldvalue></code>
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.</p></div>
<div class="paragraph"><p>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:".</p></div>
<div class="paragraph"><p>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 <strong>real</strong> 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).</p></div>
<div class="paragraph"><p>If --no-deref is given, <ref> itself is overwritten, rather than
the result of following the symbolic pointers.</p></div>
<div class="paragraph"><p>In general, using</p></div>
<div class="literalblock">
<div class="content">
<pre><code>git update-ref HEAD "$head"</code></pre>
</div></div>
<div class="paragraph"><p>should be a <em>lot</em> safer than doing</p></div>
<div class="literalblock">
<div class="content">
<pre><code>echo "$head" > "$GIT_DIR/HEAD"</code></pre>
</div></div>
<div class="paragraph"><p>both from a symlink following standpoint <strong>and</strong> an error checking
standpoint. The "refs/" rule for symlinks means that symlinks
that point to "outside" the tree are safe: they’ll be followed
for reading but not for writing (so we’ll never write through a
ref symlink to some other tree, if you have copied a whole
archive by creating a symlink tree).</p></div>
<div class="paragraph"><p>With <code>-d</code> flag, it deletes the named <ref> after verifying it
still contains <oldvalue>.</p></div>
<div class="paragraph"><p>With <code>--stdin</code>, update-ref reads instructions from standard input and
performs all modifications together. Specify commands of the form:</p></div>
<div class="literalblock">
<div class="content">
<pre><code>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</code></pre>
</div></div>
<div class="paragraph"><p>With <code>--create-reflog</code>, update-ref will create a reflog for each ref
even if one would not ordinarily be created.</p></div>
<div class="paragraph"><p>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.</p></div>
<div class="paragraph"><p>Alternatively, use <code>-z</code> to specify in NUL-terminated format, without
quoting:</p></div>
<div class="literalblock">
<div class="content">
<pre><code>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</code></pre>
</div></div>
<div class="paragraph"><p>In this format, use 40 "0" to specify a zero value, and use the empty
string to specify a missing value.</p></div>
<div class="paragraph"><p>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:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
update
</dt>
<dd>
<p>
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.
</p>
</dd>
<dt class="hdlist1">
create
</dt>
<dd>
<p>
Create <ref> with <newvalue> after verifying it does not
exist. The given <newvalue> may not be zero.
</p>
</dd>
<dt class="hdlist1">
delete
</dt>
<dd>
<p>
Delete <ref> after verifying it exists with <oldvalue>, if
given. If given, <oldvalue> may not be zero.
</p>
</dd>
<dt class="hdlist1">
verify
</dt>
<dd>
<p>
Verify <ref> against <oldvalue> but do not change it. If
<oldvalue> zero or missing, the ref must not exist.
</p>
</dd>
<dt class="hdlist1">
option
</dt>
<dd>
<p>
Modify behavior of the next command naming a <ref>.
The only valid option is <code>no-deref</code> to avoid dereferencing
a symbolic ref.
</p>
</dd>
</dl></div>
<div class="paragraph"><p>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.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_logging_updates">Logging Updates</h2>
<div class="sectionbody">
<div class="paragraph"><p>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 <code>git update-ref</code> 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:</p></div>
<div class="olist arabic"><ol class="arabic">
<li>
<p>
oldsha1 SP newsha1 SP committer LF
</p>
<div class="paragraph"><p>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’s name, email address
and date in the standard Git committer ident format.</p></div>
</li>
</ol></div>
<div class="paragraph"><p>Optionally with -m:</p></div>
<div class="olist arabic"><ol class="arabic">
<li>
<p>
oldsha1 SP newsha1 SP committer TAB message LF
</p>
<div class="paragraph"><p>Where all fields are as described above and "message" is the
value supplied to the -m option.</p></div>
</li>
</ol></div>
<div class="paragraph"><p>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.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_git">GIT</h2>
<div class="sectionbody">
<div class="paragraph"><p>Part of the <a href="git.html">git(1)</a> suite</p></div>
</div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
Last updated 2016-03-17 20:47:59 UTC
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