GIT\-UPDATE\-REFSection: Git Manual (1)
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NAMEgit-update-ref - Update the object name stored in a ref safely
SYNOPSISgit-update-ref [-m <reason>] (-d <ref> <oldvalue> | [--no-deref] <ref> <newvalue> [<oldvalue>])
DESCRIPTIONGiven 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 "$head"
echo "$head" > "$GIT_DIR/HEAD"
LOGGING UPDATESIf config parameter "core.logAllRefUpdates" is true or the file "$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.
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.
AUTHORWritten by Linus Torvalds <email@example.com>.
GITPart of the git(7) suite