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 735 <body class="manpage">
 736 <div id="header">
 737 <h1>
 738 git-update-ref(1) Manual Page
 739 </h1>
 740 <h2>NAME</h2>
 741 <div class="sectionbody">
 742 <p>git-update-ref -
 743    Update the object name stored in a ref safely
 744 </p>
 745 </div>
 746 </div>
 747 <div id="content">
 748 <div class="sect1">
 749 <h2 id="_synopsis">SYNOPSIS</h2>
 750 <div class="sectionbody">
 751 <div class="verseblock">
 752 <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>
 753 <div class="attribution">
 754 </div></div>
 755 </div>
 756 </div>
 757 <div class="sect1">
 758 <h2 id="_description">DESCRIPTION</h2>
 759 <div class="sectionbody">
 760 <div class="paragraph"><p>Given two arguments, stores the &lt;new-oid&gt; in the &lt;ref&gt;, possibly
 761 dereferencing the symbolic refs.  E.g. <code>git update-ref HEAD
 762 &lt;new-oid&gt;</code> updates the current branch head to the new object.</p></div>
 763 <div class="paragraph"><p>Given three arguments, stores the &lt;new-oid&gt; in the &lt;ref&gt;,
 764 possibly dereferencing the symbolic refs, after verifying that
 765 the current value of the &lt;ref&gt; matches &lt;old-oid&gt;.
 766 E.g. <code>git update-ref refs/heads/master &lt;new-oid&gt; &lt;old-oid&gt;</code>
 767 updates the master branch head to &lt;new-oid&gt; only if its current
 768 value is &lt;old-oid&gt;.  You can specify 40 "0" or an empty string
 769 as &lt;old-oid&gt; to make sure that the ref you are creating does
 770 not exist.</p></div>
 771 <div class="paragraph"><p>It also allows a "ref" file to be a symbolic pointer to another
 772 ref file by starting with the four-byte header sequence of
 773 "ref:".</p></div>
 774 <div class="paragraph"><p>More importantly, it allows the update of a ref file to follow
 775 these symbolic pointers, whether they are symlinks or these
 776 "regular file symbolic refs".  It follows <strong>real</strong> symlinks only
 777 if they start with "refs/": otherwise it will just try to read
 778 them and update them as a regular file (i.e. it will allow the
 779 filesystem to follow them, but will overwrite such a symlink to
 780 somewhere else with a regular filename).</p></div>
 781 <div class="paragraph"><p>If --no-deref is given, &lt;ref&gt; itself is overwritten, rather than
 782 the result of following the symbolic pointers.</p></div>
 783 <div class="paragraph"><p>In general, using</p></div>
 784 <div class="literalblock">
 785 <div class="content">
 786 <pre><code>git update-ref HEAD "$head"</code></pre>
 787 </div></div>
 788 <div class="paragraph"><p>should be a <em>lot</em> safer than doing</p></div>
 789 <div class="literalblock">
 790 <div class="content">
 791 <pre><code>echo "$head" &gt; "$GIT_DIR/HEAD"</code></pre>
 792 </div></div>
 793 <div class="paragraph"><p>both from a symlink following standpoint <strong>and</strong> an error checking
 794 standpoint.  The "refs/" rule for symlinks means that symlinks
 795 that point to "outside" the tree are safe: they&#8217;ll be followed
 796 for reading but not for writing (so we&#8217;ll never write through a
 797 ref symlink to some other tree, if you have copied a whole
 798 archive by creating a symlink tree).</p></div>
 799 <div class="paragraph"><p>With <code>-d</code> flag, it deletes the named &lt;ref&gt; after verifying it
 800 still contains &lt;old-oid&gt;.</p></div>
 801 <div class="paragraph"><p>With <code>--stdin</code>, update-ref reads instructions from standard input and
 802 performs all modifications together.  Specify commands of the form:</p></div>
 803 <div class="literalblock">
 804 <div class="content">
 805 <pre><code>update SP &lt;ref&gt; SP &lt;new-oid&gt; [SP &lt;old-oid&gt;] LF
 806 create SP &lt;ref&gt; SP &lt;new-oid&gt; LF
 807 delete SP &lt;ref&gt; [SP &lt;old-oid&gt;] LF
 808 verify SP &lt;ref&gt; [SP &lt;old-oid&gt;] LF
 809 option SP &lt;opt&gt; LF
 810 start LF
 811 prepare LF
 812 commit LF
 813 abort LF</code></pre>
 814 </div></div>
 815 <div class="paragraph"><p>With <code>--create-reflog</code>, update-ref will create a reflog for each ref
 816 even if one would not ordinarily be created.</p></div>
 817 <div class="paragraph"><p>Quote fields containing whitespace as if they were strings in C source
 818 code; i.e., surrounded by double-quotes and with backslash escapes.
 819 Use 40 "0" characters or the empty string to specify a zero value.  To
 820 specify a missing value, omit the value and its preceding SP entirely.</p></div>
 821 <div class="paragraph"><p>Alternatively, use <code>-z</code> to specify in NUL-terminated format, without
 822 quoting:</p></div>
 823 <div class="literalblock">
 824 <div class="content">
 825 <pre><code>update SP &lt;ref&gt; NUL &lt;new-oid&gt; NUL [&lt;old-oid&gt;] NUL
 826 create SP &lt;ref&gt; NUL &lt;new-oid&gt; NUL
 827 delete SP &lt;ref&gt; NUL [&lt;old-oid&gt;] NUL
 828 verify SP &lt;ref&gt; NUL [&lt;old-oid&gt;] NUL
 829 option SP &lt;opt&gt; NUL
 830 start NUL
 831 prepare NUL
 832 commit NUL
 833 abort NUL</code></pre>
 834 </div></div>
 835 <div class="paragraph"><p>In this format, use 40 "0" to specify a zero value, and use the empty
 836 string to specify a missing value.</p></div>
 837 <div class="paragraph"><p>In either format, values can be specified in any form that Git
 838 recognizes as an object name.  Commands in any other format or a
 839 repeated &lt;ref&gt; produce an error.  Command meanings are:</p></div>
 840 <div class="dlist"><dl>
 841 <dt class="hdlist1">
 842 update
 843 </dt>
 844 <dd>
 845 <p>
 846         Set &lt;ref&gt; to &lt;new-oid&gt; after verifying &lt;old-oid&gt;, if given.
 847         Specify a zero &lt;new-oid&gt; to ensure the ref does not exist
 848         after the update and/or a zero &lt;old-oid&gt; to make sure the
 849         ref does not exist before the update.
 850 </p>
 851 </dd>
 852 <dt class="hdlist1">
 853 create
 854 </dt>
 855 <dd>
 856 <p>
 857         Create &lt;ref&gt; with &lt;new-oid&gt; after verifying it does not
 858         exist.  The given &lt;new-oid&gt; may not be zero.
 859 </p>
 860 </dd>
 861 <dt class="hdlist1">
 862 delete
 863 </dt>
 864 <dd>
 865 <p>
 866         Delete &lt;ref&gt; after verifying it exists with &lt;old-oid&gt;, if
 867         given.  If given, &lt;old-oid&gt; may not be zero.
 868 </p>
 869 </dd>
 870 <dt class="hdlist1">
 871 verify
 872 </dt>
 873 <dd>
 874 <p>
 875         Verify &lt;ref&gt; against &lt;old-oid&gt; but do not change it.  If
 876         &lt;old-oid&gt; is zero or missing, the ref must not exist.
 877 </p>
 878 </dd>
 879 <dt class="hdlist1">
 880 option
 881 </dt>
 882 <dd>
 883 <p>
 884         Modify the behavior of the next command naming a &lt;ref&gt;.
 885         The only valid option is <code>no-deref</code> to avoid dereferencing
 886         a symbolic ref.
 887 </p>
 888 </dd>
 889 <dt class="hdlist1">
 890 start
 891 </dt>
 892 <dd>
 893 <p>
 894         Start a transaction. In contrast to a non-transactional session, a
 895         transaction will automatically abort if the session ends without an
 896         explicit commit. This command may create a new empty transaction when
 897         the current one has been committed or aborted already.
 898 </p>
 899 </dd>
 900 <dt class="hdlist1">
 901 prepare
 902 </dt>
 903 <dd>
 904 <p>
 905         Prepare to commit the transaction. This will create lock files for all
 906         queued reference updates. If one reference could not be locked, the
 907         transaction will be aborted.
 908 </p>
 909 </dd>
 910 <dt class="hdlist1">
 911 commit
 912 </dt>
 913 <dd>
 914 <p>
 915         Commit all reference updates queued for the transaction, ending the
 916         transaction.
 917 </p>
 918 </dd>
 919 <dt class="hdlist1">
 920 abort
 921 </dt>
 922 <dd>
 923 <p>
 924         Abort the transaction, releasing all locks if the transaction is in
 925         prepared state.
 926 </p>
 927 </dd>
 928 </dl></div>
 929 <div class="paragraph"><p>If all &lt;ref&gt;s can be locked with matching &lt;old-oid&gt;s
 930 simultaneously, all modifications are performed.  Otherwise, no
 931 modifications are performed.  Note that while each individual
 932 &lt;ref&gt; is updated or deleted atomically, a concurrent reader may
 933 still see a subset of the modifications.</p></div>
 934 </div>
 935 </div>
 936 <div class="sect1">
 937 <h2 id="_logging_updates">LOGGING UPDATES</h2>
 938 <div class="sectionbody">
 939 <div class="paragraph"><p>If config parameter "core.logAllRefUpdates" is true and the ref is one
 940 under "refs/heads/", "refs/remotes/", "refs/notes/", or a pseudoref
 941 like HEAD or ORIG_HEAD; or the file "$GIT_DIR/logs/&lt;ref&gt;" exists then
 942 <code>git update-ref</code> will append a line to the log file
 943 "$GIT_DIR/logs/&lt;ref&gt;" (dereferencing all symbolic refs before creating
 944 the log name) describing the change in ref value.  Log lines are
 945 formatted as:</p></div>
 946 <div class="literalblock">
 947 <div class="content">
 948 <pre><code>oldsha1 SP newsha1 SP committer LF</code></pre>
 949 </div></div>
 950 <div class="paragraph"><p>Where "oldsha1" is the 40 character hexadecimal value previously
 951 stored in &lt;ref&gt;, "newsha1" is the 40 character hexadecimal value of
 952 &lt;new-oid&gt; and "committer" is the committer&#8217;s name, email address
 953 and date in the standard Git committer ident format.</p></div>
 954 <div class="paragraph"><p>Optionally with -m:</p></div>
 955 <div class="literalblock">
 956 <div class="content">
 957 <pre><code>oldsha1 SP newsha1 SP committer TAB message LF</code></pre>
 958 </div></div>
 959 <div class="paragraph"><p>Where all fields are as described above and "message" is the
 960 value supplied to the -m option.</p></div>
 961 <div class="paragraph"><p>An update will fail (without changing &lt;ref&gt;) if the current user is
 962 unable to create a new log file, append to the existing log file
 963 or does not have committer information available.</p></div>
 964 </div>
 965 </div>
 966 <div class="sect1">
 967 <h2 id="_git">GIT</h2>
 968 <div class="sectionbody">
 969 <div class="paragraph"><p>Part of the <a href="git.html">git(1)</a> suite</p></div>
 970 </div>
 971 </div>
 972 </div>
 973 <div id="footnotes"><hr /></div>
 974 <div id="footer">
 975 <div id="footer-text">
 976 Last updated
 977  2024-04-10 12:46:30 PDT
 978 </div>
 979 </div>
 980 </body>
 981 </html>