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
create
delete
symref-update
verify
symref-create: Create symbolic ref <ref> with <new-target> after verifying it does not exist.
symref-delete
symref-verify
option
start
prepare
commit
abort
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
11/25/2024 | Git 2.47.1 |