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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | LOGGING UPDATES | GIT | COLOPHON |
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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> [<old-oid>] | [--create-reflog] <ref> <new-oid> [<old-oid>] | --stdin [-z])
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
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:
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.
verify
Verify <ref> against <old-oid> but do not change it. If
<old-oid> is zero or missing, the ref must not exist.
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.
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.
Part of the git(1) suite
This page is part of the git (Git distributed version control
system) project. Information about the project can be found at
⟨http://git-scm.com/⟩. If you have a bug report for this manual
page, see ⟨http://git-scm.com/community⟩. This page was obtained
from the project's upstream Git repository
⟨https://github.com/git/git.git⟩ 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
[email protected]
Git 2.45.2.492.gd63586 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)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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