6 git-update-ref - Update the object name stored in a ref safely
11 'git update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>])
15 Given two arguments, stores the <newvalue> in the <ref>, possibly
16 dereferencing the symbolic refs. E.g. `git update-ref HEAD
17 <newvalue>` updates the current branch head to the new object.
19 Given three arguments, stores the <newvalue> in the <ref>,
20 possibly dereferencing the symbolic refs, after verifying that
21 the current value of the <ref> matches <oldvalue>.
22 E.g. `git update-ref refs/heads/master <newvalue> <oldvalue>`
23 updates the master branch head to <newvalue> only if its current
24 value is <oldvalue>. You can specify 40 "0" or an empty string
25 as <oldvalue> to make sure that the ref you are creating does
28 It also allows a "ref" file to be a symbolic pointer to another
29 ref file by starting with the four-byte header sequence of
32 More importantly, it allows the update of a ref file to follow
33 these symbolic pointers, whether they are symlinks or these
34 "regular file symbolic refs". It follows *real* symlinks only
35 if they start with "refs/": otherwise it will just try to read
36 them and update them as a regular file (i.e. it will allow the
37 filesystem to follow them, but will overwrite such a symlink to
38 somewhere else with a regular filename).
40 If --no-deref is given, <ref> itself is overwritten, rather than
41 the result of following the symbolic pointers.
45 git update-ref HEAD "$head"
47 should be a _lot_ safer than doing
49 echo "$head" > "$GIT_DIR/HEAD"
51 both from a symlink following standpoint *and* an error checking
52 standpoint. The "refs/" rule for symlinks means that symlinks
53 that point to "outside" the tree are safe: they'll be followed
54 for reading but not for writing (so we'll never write through a
55 ref symlink to some other tree, if you have copied a whole
56 archive by creating a symlink tree).
58 With `-d` flag, it deletes the named <ref> after verifying it
59 still contains <oldvalue>.
64 If config parameter "core.logAllRefUpdates" is true and the ref is one under
65 "refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic ref HEAD; or
66 the file "$GIT_DIR/logs/<ref>" exists then `git update-ref` will append
67 a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all
68 symbolic refs before creating the log name) describing the change
69 in ref value. Log lines are formatted as:
71 . oldsha1 SP newsha1 SP committer LF
73 Where "oldsha1" is the 40 character hexadecimal value previously
74 stored in <ref>, "newsha1" is the 40 character hexadecimal value of
75 <newvalue> and "committer" is the committer's name, email address
76 and date in the standard GIT committer ident format.
80 . oldsha1 SP newsha1 SP committer TAB message LF
82 Where all fields are as described above and "message" is the
83 value supplied to the -m option.
85 An update will fail (without changing <ref>) if the current user is
86 unable to create a new log file, append to the existing log file
87 or does not have committer information available.
91 Part of the linkgit:git[1] suite