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<body class="manpage">
<div id="header">
<h1>git-update-ref(1) Manual Page</h1>
<h2 id="_name">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 &lt;reason&gt;] [--no-deref] (-d &lt;ref&gt; [&lt;old-oid&gt;] | [--create-reflog] &lt;ref&gt; &lt;new-oid&gt; [&lt;old-oid&gt;] | --stdin [-z])</pre>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Given two arguments, stores the &lt;new-oid&gt; in the &lt;ref&gt;, possibly
dereferencing the symbolic refs.  E.g. <code>git</code> <code>update-ref</code> <code>HEAD</code>
<em>&lt;new-oid&gt;</em> updates the current branch head to the new object.</p>
</div>
<div class="paragraph">
<p>Given three arguments, stores the &lt;new-oid&gt; in the &lt;ref&gt;,
possibly dereferencing the symbolic refs, after verifying that
the current value of the &lt;ref&gt; matches &lt;old-oid&gt;.
E.g. <code>git</code> <code>update-ref</code> <code>refs/heads/master</code> <em>&lt;new-oid&gt;</em> <em>&lt;old-oid&gt;</em>
updates the master branch head to &lt;new-oid&gt; only if its current
value is &lt;old-oid&gt;.  You can specify 40 "0" or an empty string
as &lt;old-oid&gt; to make sure that the ref you are creating does
not exist.</p>
</div>
<div class="paragraph">
<p>The final arguments are object names; this command without any options
does not support updating a symbolic ref to point to another ref (see
<a href="git-symbolic-ref.html">git-symbolic-ref(1)</a>).  But <code>git</code> <code>update-ref</code> <code>--stdin</code> does have
the <code>symref-</code>* commands so that regular refs and symbolic refs can be
committed in the same transaction.</p>
</div>
<div class="paragraph">
<p>If --no-deref is given, &lt;ref&gt; itself is overwritten, rather than
the result of following the symbolic pointers.</p>
</div>
<div class="paragraph">
<p>With <code>-d</code>, it deletes the named &lt;ref&gt; after verifying that it
still contains &lt;old-oid&gt;.</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>update SP &lt;ref&gt; SP &lt;new-oid&gt; [SP &lt;old-oid&gt;] LF
create SP &lt;ref&gt; SP &lt;new-oid&gt; LF
delete SP &lt;ref&gt; [SP &lt;old-oid&gt;] LF
verify SP &lt;ref&gt; [SP &lt;old-oid&gt;] LF
symref-update SP &lt;ref&gt; SP &lt;new-target&gt; [SP (ref SP &lt;old-target&gt; | oid SP &lt;old-oid&gt;)] LF
symref-create SP &lt;ref&gt; SP &lt;new-target&gt; LF
symref-delete SP &lt;ref&gt; [SP &lt;old-target&gt;] LF
symref-verify SP &lt;ref&gt; [SP &lt;old-target&gt;] LF
option SP &lt;opt&gt; LF
start LF
prepare LF
commit LF
abort LF</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>update SP &lt;ref&gt; NUL &lt;new-oid&gt; NUL [&lt;old-oid&gt;] NUL
create SP &lt;ref&gt; NUL &lt;new-oid&gt; NUL
delete SP &lt;ref&gt; NUL [&lt;old-oid&gt;] NUL
verify SP &lt;ref&gt; NUL [&lt;old-oid&gt;] NUL
symref-update SP &lt;ref&gt; NUL &lt;new-target&gt; [NUL (ref NUL &lt;old-target&gt; | oid NUL &lt;old-oid&gt;)] NUL
symref-create SP &lt;ref&gt; NUL &lt;new-target&gt; NUL
symref-delete SP &lt;ref&gt; [NUL &lt;old-target&gt;] NUL
symref-verify SP &lt;ref&gt; [NUL &lt;old-target&gt;] NUL
option SP &lt;opt&gt; NUL
start NUL
prepare NUL
commit NUL
abort NUL</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 &lt;ref&gt; produce an error.  Command meanings are:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1">update</dt>
<dd>
<p>Set &lt;ref&gt; to &lt;new-oid&gt; after verifying &lt;old-oid&gt;, if given.
Specify a zero &lt;new-oid&gt; to ensure the ref does not exist
after the update and/or a zero &lt;old-oid&gt; to make sure the
ref does not exist before the update.</p>
</dd>
<dt class="hdlist1">create</dt>
<dd>
<p>Create &lt;ref&gt; with &lt;new-oid&gt; after verifying that it does not
exist.  The given &lt;new-oid&gt; may not be zero.</p>
</dd>
<dt class="hdlist1">delete</dt>
<dd>
<p>Delete &lt;ref&gt; after verifying that it exists with &lt;old-oid&gt;, if
given.  If given, &lt;old-oid&gt; may not be zero.</p>
</dd>
<dt class="hdlist1">symref-update</dt>
<dd>
<p>Set &lt;ref&gt; to &lt;new-target&gt; after verifying &lt;old-target&gt; or &lt;old-oid&gt;,
if given. Specify a zero &lt;old-oid&gt; to ensure that the ref does not
exist before the update.</p>
</dd>
<dt class="hdlist1">verify</dt>
<dd>
<p>Verify &lt;ref&gt; against &lt;old-oid&gt; but do not change it.  If
&lt;old-oid&gt; is zero or missing, the ref must not exist.</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>symref-create:
	Create symbolic ref &lt;ref&gt; with &lt;new-target&gt; after verifying that
	it does not exist.</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1">symref-delete</dt>
<dd>
<p>Delete &lt;ref&gt; after verifying that it exists with &lt;old-target&gt;, if given.</p>
</dd>
<dt class="hdlist1">symref-verify</dt>
<dd>
<p>Verify symbolic &lt;ref&gt; against &lt;old-target&gt; but do not change it.
If &lt;old-target&gt; is missing, the ref must not exist.  Can only be
used in <code>no-deref</code> mode.</p>
</dd>
<dt class="hdlist1">option</dt>
<dd>
<p>Modify the behavior of the next command naming a &lt;ref&gt;.
The only valid option is <code>no-deref</code> to avoid dereferencing
a symbolic ref.</p>
</dd>
<dt class="hdlist1">start</dt>
<dd>
<p>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.</p>
</dd>
<dt class="hdlist1">prepare</dt>
<dd>
<p>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.</p>
</dd>
<dt class="hdlist1">commit</dt>
<dd>
<p>Commit all reference updates queued for the transaction, ending the
transaction.</p>
</dd>
<dt class="hdlist1">abort</dt>
<dd>
<p>Abort the transaction, releasing all locks if the transaction is in
prepared state.</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>If all &lt;ref&gt;s can be locked with matching &lt;old-oid&gt;s
simultaneously, all modifications are performed.  Otherwise, no
modifications are performed.  Note that while each individual
&lt;ref&gt; 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 a pseudoref
like HEAD or ORIG_HEAD; or the file "$GIT_DIR/logs/&lt;ref&gt;" exists then
<code>git</code> <code>update-ref</code> will append a line to the log file
"$GIT_DIR/logs/&lt;ref&gt;" (dereferencing all symbolic refs before creating
the log name) describing the change in ref value.  Log lines are
formatted as:</p>
</div>
<div class="literalblock">
<div class="content">
<pre>oldsha1 SP newsha1 SP committer LF</pre>
</div>
</div>
<div class="paragraph">
<p>Where "oldsha1" is the 40 character hexadecimal value previously
stored in &lt;ref&gt;, "newsha1" is the 40 character hexadecimal value of
&lt;new-oid&gt; and "committer" is the committer&#8217;s name, email address
and date in the standard Git committer ident format.</p>
</div>
<div class="paragraph">
<p>Optionally with -m:</p>
</div>
<div class="literalblock">
<div class="content">
<pre>oldsha1 SP newsha1 SP committer TAB message LF</pre>
</div>
</div>
<div class="paragraph">
<p>Where all fields are as described above and "message" is the
value supplied to the -m option.</p>
</div>
<div class="paragraph">
<p>An update will fail (without changing &lt;ref&gt;) 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="_notes">NOTES</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Symbolic refs were initially implemented using symbolic links.  This is
now deprecated since not all filesystems support symbolic links.</p>
</div>
<div class="paragraph">
<p>This command 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>
</div>
<div class="sect1">
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph">
<p><a href="git-symbolic-ref.html">git-symbolic-ref(1)</a></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>
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