6 git-update-ref - Update the object name stored in a ref safely
11 'git update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] [--create-reflog] <ref> <newvalue> [<oldvalue>] | --stdin [-z])
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>.
61 With `--stdin`, update-ref reads instructions from standard input and
62 performs all modifications together. Specify commands of the form:
64 update SP <ref> SP <newvalue> [SP <oldvalue>] LF
65 create SP <ref> SP <newvalue> LF
66 delete SP <ref> [SP <oldvalue>] LF
67 verify SP <ref> [SP <oldvalue>] LF
70 With `--create-reflog`, update-ref will create a reflog for each ref
71 even if one would not ordinarily be created.
73 Quote fields containing whitespace as if they were strings in C source
74 code; i.e., surrounded by double-quotes and with backslash escapes.
75 Use 40 "0" characters or the empty string to specify a zero value. To
76 specify a missing value, omit the value and its preceding SP entirely.
78 Alternatively, use `-z` to specify in NUL-terminated format, without
81 update SP <ref> NUL <newvalue> NUL [<oldvalue>] NUL
82 create SP <ref> NUL <newvalue> NUL
83 delete SP <ref> NUL [<oldvalue>] NUL
84 verify SP <ref> NUL [<oldvalue>] NUL
87 In this format, use 40 "0" to specify a zero value, and use the empty
88 string to specify a missing value.
90 In either format, values can be specified in any form that Git
91 recognizes as an object name. Commands in any other format or a
92 repeated <ref> produce an error. Command meanings are:
95 Set <ref> to <newvalue> after verifying <oldvalue>, if given.
96 Specify a zero <newvalue> to ensure the ref does not exist
97 after the update and/or a zero <oldvalue> to make sure the
98 ref does not exist before the update.
101 Create <ref> with <newvalue> after verifying it does not
102 exist. The given <newvalue> may not be zero.
105 Delete <ref> after verifying it exists with <oldvalue>, if
106 given. If given, <oldvalue> may not be zero.
109 Verify <ref> against <oldvalue> but do not change it. If
110 <oldvalue> zero or missing, the ref must not exist.
113 Modify behavior of the next command naming a <ref>.
114 The only valid option is `no-deref` to avoid dereferencing
117 If all <ref>s can be locked with matching <oldvalue>s
118 simultaneously, all modifications are performed. Otherwise, no
119 modifications are performed. Note that while each individual
120 <ref> is updated or deleted atomically, a concurrent reader may
121 still see a subset of the modifications.
125 If config parameter "core.logAllRefUpdates" is true and the ref is one under
126 "refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic ref HEAD; or
127 the file "$GIT_DIR/logs/<ref>" exists then `git update-ref` will append
128 a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all
129 symbolic refs before creating the log name) describing the change
130 in ref value. Log lines are formatted as:
132 . oldsha1 SP newsha1 SP committer LF
134 Where "oldsha1" is the 40 character hexadecimal value previously
135 stored in <ref>, "newsha1" is the 40 character hexadecimal value of
136 <newvalue> and "committer" is the committer's name, email address
137 and date in the standard Git committer ident format.
141 . oldsha1 SP newsha1 SP committer TAB message LF
143 Where all fields are as described above and "message" is the
144 value supplied to the -m option.
146 An update will fail (without changing <ref>) if the current user is
147 unable to create a new log file, append to the existing log file
148 or does not have committer information available.
152 Part of the linkgit:git[1] suite