6 git-update-ref - Update the object name stored in a ref safely
11 'git update-ref' [-m <reason>] [--no-deref] (-d <ref> [<oldvalue>] | [--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