git-update-ref(1) — Linux manual page


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>] [--no-deref] (-d <ref> [<old-oid>] | [--create-reflog] <ref> <new-oid> [<old-oid>] | --stdin [-z])

DESCRIPTION         top

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

       Given three arguments, stores the <new-oid> in the <ref>,
       possibly dereferencing the symbolic refs, after verifying that
       the current value of the <ref> matches <old-oid>. E.g. git
       update-ref refs/heads/master <new-oid> <old-oid> updates the
       master branch head to <new-oid> only if its current value is
       <old-oid>. You can specify 40 "0" or an empty string as <old-oid>
       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

       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 <old-oid>.

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

           update SP <ref> SP <new-oid> [SP <old-oid>] LF
           create SP <ref> SP <new-oid> LF
           delete SP <ref> [SP <old-oid>] LF
           verify SP <ref> [SP <old-oid>] LF
           option SP <opt> LF
           start LF
           prepare LF
           commit LF
           abort 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 <new-oid> NUL [<old-oid>] NUL
           create SP <ref> NUL <new-oid> NUL
           delete SP <ref> NUL [<old-oid>] NUL
           verify SP <ref> NUL [<old-oid>] NUL
           option SP <opt> NUL
           start NUL
           prepare NUL
           commit NUL
           abort 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:

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

           Create <ref> with <new-oid> after verifying it does not
           exist. The given <new-oid> may not be zero.

           Delete <ref> after verifying it exists with <old-oid>, if
           given. If given, <old-oid> may not be zero.

           Verify <ref> against <old-oid> but do not change it. If
           <old-oid> is zero or missing, the ref must not exist.

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

           Start a transaction. In contrast to a non-transactional
           session, a transaction will automatically abort if the
           session ends without an explicit commit. This command may
           create a new empty transaction when the current one has been
           committed or aborted already.

           Prepare to commit the transaction. This will create lock
           files for all queued reference updates. If one reference
           could not be locked, the transaction will be aborted.

           Commit all reference updates queued for the transaction,
           ending the transaction.

           Abort the transaction, releasing all locks if the transaction
           is in prepared state.

       If all <ref>s can be locked with matching <old-oid>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.


       If config parameter "core.logAllRefUpdates" is true and the ref
       is one under "refs/heads/", "refs/remotes/", "refs/notes/", or a
       pseudoref like HEAD or ORIG_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:

           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 <new-oid> and "committer" is the committer’s name, email
       address and date in the standard Git committer ident format.

       Optionally with -m:

           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
       ⟨⟩.  If you have a bug report for this manual
       page, see ⟨⟩.  This page was obtained
       from the project's upstream Git repository
       ⟨⟩ on 2024-06-14.  (At that time,
       the date of the most recent commit that was found in the
       repository was 2024-06-12.)  If you discover any rendering
       problems in this HTML version 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 manual page), send a mail to

Git         2024-06-12              GIT-UPDATE-REF(1)

Pages that refer to this page: git(1)git-merge-tree(1)git-show-ref(1)git-worktree(1)gitrepository-layout(5)gitglossary(7)