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} div.exampleblock-content { border-left: 2px solid silver; padding-left: 0.5em; } /* IE6 sets dynamically generated links as visited. */ div#toc a:visited { color: blue; } </style> </head> <body> <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> <h2 id="_synopsis">SYNOPSIS</h2> <div class="sectionbody"> <div class="paragraph"><p><em>git update-ref</em> [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>])</p></div> </div> <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. <tt>git update-ref HEAD <newvalue></tt> 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. <tt>git update-ref refs/heads/master <newvalue> <oldvalue></tt> 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><tt>git update-ref HEAD "$head"</tt></pre> </div></div> <div class="paragraph"><p>should be a <em>lot</em> safer than doing</p></div> <div class="literalblock"> <div class="content"> <pre><tt>echo "$head" > "$GIT_DIR/HEAD"</tt></pre> </div></div> <div class="paragraph"><p>both from a symlink following standpoint <strong>and</strong> an error checking standpoint. The "refs/" rule for symlinks means that symlinks that point to "outside" the tree are safe: they’ll be followed for reading but not for writing (so we’ll never write through a ref symlink to some other tree, if you have copied a whole archive by creating a symlink tree).</p></div> <div class="paragraph"><p>With <tt>-d</tt> flag, it deletes the named <ref> after verifying it still contains <oldvalue>.</p></div> </div> <h2 id="_logging_updates">Logging Updates</h2> <div class="sectionbody"> <div class="paragraph"><p>If config parameter "core.logAllRefUpdates" is true or the file "$GIT_DIR/logs/<ref>" exists then <tt>git update-ref</tt> 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> <h2 id="_author">Author</h2> <div class="sectionbody"> <div class="paragraph"><p>Written by Linus Torvalds <<a href="mailto:torvalds@osdl.org">torvalds@osdl.org</a>>.</p></div> </div> <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 id="footer"> <div id="footer-text"> Last updated 2010-12-16 02:52:11 UTC </div> </div> </body> </html>