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.

The final arguments are object names; this command without any
options does not support updating a symbolic ref to point to another
ref (see git-symbolic-ref(1)). But git update-ref --stdin does have
the symref-* commands so that regular refs and symbolic refs can be
committed in the same transaction.

If --no-deref is given, <ref> itself is overwritten, rather than the
result of following the symbolic pointers.

With -d, it deletes the named <ref> after verifying that 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 that it does not
exist. The given <new-oid> may not be zero.

delete
Delete <ref> after verifying that 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 that it does not exist.

symref-delete
Delete <ref> after verifying that 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.

NOTES

Symbolic refs were initially implemented using symbolic links. This
is now deprecated since not all filesystems support symbolic links.

This command 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).

SEE ALSO

git-symbolic-ref(1)

GIT

Part of the git(1) suite

Git 2.48.1 2025-01-13 GIT-UPDATE-REF(1)