git-update-ref - Update the object name stored in a ref safely
git update-ref [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>])
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>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>])
DESCRIPTION
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" > "$GIT_DIR/HEAD"
both from a symlink following standpoint and an error checking
standpoint. The "refs/" rule for symlinks means that symlinks that
point to "outside" the tree are safe: they'll be followed for reading
but not for writing (so we'll never write through a ref symlink to some
other tree, if you have copied a whole archive by creating a symlink
tree).
With -d flag, it deletes the named <ref> after verifying it still
contains <oldvalue>.
LOGGING UPDATES
If config parameter "core.logAllRefUpdates" is true and the ref is one
under "refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic
ref HEAD; or the file "$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.
GIT
Part of the git(1) suite
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+---------------+--------------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+--------------------------+
|Availability | developer/versioning/git |
+---------------+--------------------------+
|Stability | Uncommitted |
+---------------+--------------------------+
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original community
source was downloaded from http://git-
core.googlecode.com/files/git-1.7.9.2.tar.gz
Further information about this software can be found on the open source
community website at http://git-scm.com/.
Git 1.7.9.2 02/22/2012 GIT-UPDATE-REF(1)