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NAME | SYNOPSIS | DESCRIPTION | LOGGING UPDATES | GIT | COLOPHON |
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>] (-d <ref> [<oldvalue>] | [--no-deref] [--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
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 <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
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 <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
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 <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
Create <ref> with <newvalue> after verifying it does not exist.
The given <newvalue> may not be zero.
delete
Delete <ref> after verifying it exists with <oldvalue>, if given.
If given, <oldvalue> may not be zero.
verify
Verify <ref> against <oldvalue> but do not change it. If
<oldvalue> zero or missing, the ref must not exist.
option
Modify behavior of the next command naming a <ref>. The only
valid option is no-deref to avoid dereferencing a symbolic ref.
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
modifications.
If config parameter "core.logAllRefUpdates" is true and the ref is
one under "refs/heads/", "refs/remotes/", "refs/notes/", or the
symbolic ref 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:
1. 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:
1. 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
2017-07-05. If you discover any rendering problems in this HTML ver‐
sion 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 man‐
ual page), send a mail to man-pages@man7.org
Git 2.7.0.rc1.5.gf3a 12/17/2015 GIT-UPDATE-REF(1)
Pages that refer to this page: git(1), git-show-ref(1), gitrepository-layout(5)