GIT-UPDATE-REF(1)                                          Git Manual                                          GIT-UPDATE-REF(1)



NAME
       git-update-ref - Update the object name stored in a ref safely

SYNOPSIS
       git update-ref [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>])

DESCRIPTION
       Given two arguments, stores the <newvalue> in the <ref>, possibly dereferencing the symbolic refs. E.g. git update-ref
       HEAD <newvalue> updates the current branch head to the new object.

       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. git update-ref refs/heads/master <newvalue> <oldvalue> 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.

       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:".

       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 real 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).

       If --no-deref is given, <ref> itself is overwritten, rather than the result of following the symbolic pointers.

       In general, using

           git update-ref HEAD "$head"

       should be a lot safer than doing

           echo "$head" > "$GIT_DIR/HEAD"

       both from a symlink following standpoint and 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).

       With -d flag, it deletes the named <ref> after verifying it still contains <oldvalue>.

LOGGING UPDATES
       If config parameter "core.logAllRefUpdates" is true or the file "$GIT_DIR/logs/<ref>" exists then git update-ref will
       append a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all symbolic refs before creating the log name)
       describing the change in ref value. Log lines are formatted as:

        1. oldsha1 SP newsha1 SP committer LF

           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.

       Optionally with -m:

        1. oldsha1 SP newsha1 SP committer TAB message LF

           Where all fields are as described above and "message" is the value supplied to the -m option.

       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.

AUTHOR
       Written by Linus Torvalds <torvaldsATosdl.org[1]>.

GIT
       Part of the git(1) suite

NOTES
        1. torvaldsATosdl.org
           mailto:torvaldsATosdl.org



Git 1.7.4.4                                                04/11/2011                                          GIT-UPDATE-REF(1)