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20 .TH "GIT-UPDATE-REF" 1 "" "" ""
22 git-update-ref \- update the object name stored in a ref safely
26 \fIgit\-update\-ref\fR [\-m <reason>] <ref> <newvalue> [<oldvalue>]
31 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\&.
34 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>\&.
37 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:"\&.
40 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 \fIreal\fR 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)\&.
46 git\-update\-ref HEAD "$head"
50 should be a _lot_ safer than doing
53 echo "$head" > "$GIT_DIR/HEAD"
57 both from a symlink following standpoint \fIand\fR an error checking standpoint\&. The "refs/" rule for symlinks means that symlinks that point to "outside" the tree are safe: they'll be followed for reading but not for writing (so we'll never write through a ref symlink to some other tree, if you have copied a whole archive by creating a symlink tree)\&.
62 If config parameter "core\&.logAllRefUpdates" is true or the file "$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:
66 oldsha1 SP newsha1 SP committer LF
68 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\&.
76 oldsha1 SP newsha1 SP committer TAB message LF
78 Where all fields are as described above and "message" is the value supplied to the \-m option\&.
82 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\&.
87 Written by Linus Torvalds <torvalds@osdl\&.org>\&.
92 Part of the \fBgit\fR(7) suite