NAME | SYNOPSIS | DESCRIPTION | LOGGING UPDATES | GIT | COLOPHON

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

NAME         top

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

SYNOPSIS         top

       git update-ref [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] [--create-reflog] <ref> <newvalue> [<oldvalue>] | --stdin [-z])

DESCRIPTION         top

       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>.

       With --stdin, update-ref reads instructions from standard input and
       performs all modifications together. Specify commands of the form:

           update SP <ref> SP <newvalue> [SP <oldvalue>] LF
           create SP <ref> SP <newvalue> LF
           delete SP <ref> [SP <oldvalue>] LF
           verify SP <ref> [SP <oldvalue>] LF
           option SP <opt> LF

       With --create-reflog, update-ref will create a reflog for each ref
       even if one would not ordinarily be created.

       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.

       Alternatively, use -z to specify in NUL-terminated format, without
       quoting:

           update SP <ref> NUL <newvalue> NUL [<oldvalue>] NUL
           create SP <ref> NUL <newvalue> NUL
           delete SP <ref> NUL [<oldvalue>] NUL
           verify SP <ref> NUL [<oldvalue>] NUL
           option SP <opt> NUL

       In this format, use 40 "0" to specify a zero value, and use the empty
       string to specify a missing value.

       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 <ref> produce an error. Command meanings are:

       update
           Set <ref> to <newvalue> after verifying <oldvalue>, if given.
           Specify a zero <newvalue> to ensure the ref does not exist after
           the update and/or a zero <oldvalue> to make sure the ref does not
           exist before the update.

       create
           Create <ref> with <newvalue> after verifying it does not exist.
           The given <newvalue> may not be zero.

       delete
           Delete <ref> after verifying it exists with <oldvalue>, if given.
           If given, <oldvalue> may not be zero.

       verify
           Verify <ref> against <oldvalue> but do not change it. If
           <oldvalue> zero or missing, the ref must not exist.

       option
           Modify behavior of the next command naming a <ref>. The only
           valid option is no-deref to avoid dereferencing a symbolic ref.

       If all <ref>s can be locked with matching <oldvalue>s simultaneously,
       all modifications are performed. Otherwise, no modifications are
       performed. Note that while each individual <ref> is updated or
       deleted atomically, a concurrent reader may still see a subset of the
       modifications.

LOGGING UPDATES         top

       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         top

       Part of the git(1) suite

COLOPHON         top

       This page is part of the git (Git distributed version control system)
       project.  Information about the project can be found at 
       ⟨http://git-scm.com/⟩.  If you have a bug report for this manual page,
       see ⟨http://git-scm.com/community⟩.  This page was obtained from the
       project's upstream Git repository ⟨https://github.com/git/git.git⟩ on
       2017-04-25.  If you discover any rendering problems in this HTML ver‐
       sion of the page, or you believe there is a better or more up-to-date
       source for the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original man‐
       ual page), send a mail to man-pages@man7.org

Git 2.7.0.rc1.5.gf3a             12/17/2015                GIT-UPDATE-REF(1)

Pages that refer to this page: git(1)git-show-ref(1)gitrepository-layout(5)