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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" > "$GIT_DIR/HEAD"
       both from a symlink following standpoint and an error checking
       standpoint. The "refs/" rule for symlinks means that symlinks that
       point to "outside" the tree are safe: they'll be followed for reading
       but not for writing (so we'll never write through a ref symlink to some
       other tree, if you have copied a whole archive by creating a symlink
       tree).
       With -d flag, it deletes the named <ref> after verifying it still
       contains <oldvalue>.
LOGGING UPDATES
       If config parameter "core.logAllRefUpdates" is true and the ref is one
       under "refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic
       ref HEAD; or the file "$GIT_DIR/logs/<ref>" exists then 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.
GIT
       Part of the git(1) suite

Git 1.8.3.1                       05/23/2023                 GIT-UPDATE-REF(1)