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>] [--no-deref] (-d <ref> [<old-oid>] | [--create-reflog] <ref> <new-oid> [<old-oid>] | --stdin [-z])
DESCRIPTION
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 "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 <old-oid>.
With --stdin, update-ref reads instructions from standard input and
performs all modifications together. Specify commands of the form:
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
symref-update SP <ref> SP <new-target> [SP (ref SP <old-target> | oid SP <old-oid>)] LF
symref-create SP <ref> SP <new-target> LF
symref-delete SP <ref> [SP <old-target>] LF
symref-verify SP <ref> [SP <old-target>] 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
symref-update SP <ref> NUL <new-target> [NUL (ref NUL <old-target> | oid NUL <old-oid>)] NUL
symref-create SP <ref> NUL <new-target> NUL
symref-delete SP <ref> [NUL <old-target>] NUL
symref-verify SP <ref> [NUL <old-target>] 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:
update
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
Create <ref> with <new-oid> after verifying it does not exist. The
given <new-oid> may not be zero.
delete
Delete <ref> after verifying it exists with <old-oid>, if given. If
given, <old-oid> may not be zero.
symref-update
Set <ref> to <new-target> after verifying <old-target> or
<old-oid>, if given. Specify a zero <old-oid> to ensure that the
ref does not exist before the update.
verify
Verify <ref> against <old-oid> but do not change it. If <old-oid>
is zero or missing, the ref must not exist.
symref-create: Create symbolic ref <ref> with <new-target> after
verifying it does not exist.
symref-delete
Delete <ref> after verifying it exists with <old-target>, if given.
symref-verify
Verify symbolic <ref> against <old-target> but do not change it. If
<old-target> is missing, the ref must not exist. Can only be used
in no-deref mode.
option
Modify the behavior of the next command naming a <ref>. The only
valid option is no-deref to avoid dereferencing a symbolic ref.
start
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
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
Commit all reference updates queued for the transaction, ending the
transaction.
abort
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.
LOGGING UPDATES
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
Part of the git(1) suite
Git 2.46.0 2024-07-29 git-update-ref(1)
git 2.46.0 - Generated Sat Aug 17 16:35:58 CDT 2024