git-update-ref manpage

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

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

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

       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

       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

       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
	   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

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

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

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

	   Modify 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

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

       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

       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 <newvalue>
       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.

       Part of the git(1) suite

Git 2.38.4			  05/16/2024		     GIT-UPDATE-REF(1)