6 git-update-ref - Update the object name stored in a ref safely
11 'git update-ref' [-m <reason>] [--no-deref] (-d <ref> [<old-oid>] | [--create-reflog] <ref> <new-oid> [<old-oid>] | --stdin [-z])
15 Given two arguments, stores the <new-oid> in the <ref>, possibly
16 dereferencing the symbolic refs. E.g. `git update-ref HEAD
17 <new-oid>` updates the current branch head to the new object.
19 Given three arguments, stores the <new-oid> in the <ref>,
20 possibly dereferencing the symbolic refs, after verifying that
21 the current value of the <ref> matches <old-oid>.
22 E.g. `git update-ref refs/heads/master <new-oid> <old-oid>`
23 updates the master branch head to <new-oid> only if its current
24 value is <old-oid>. You can specify 40 "0" or an empty string
25 as <old-oid> 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 <old-oid>.
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 <new-oid> [SP <old-oid>] LF
65 create SP <ref> SP <new-oid> LF
66 delete SP <ref> [SP <old-oid>] LF
67 verify SP <ref> [SP <old-oid>] LF
74 With `--create-reflog`, update-ref will create a reflog for each ref
75 even if one would not ordinarily be created.
77 Quote fields containing whitespace as if they were strings in C source
78 code; i.e., surrounded by double-quotes and with backslash escapes.
79 Use 40 "0" characters or the empty string to specify a zero value. To
80 specify a missing value, omit the value and its preceding SP entirely.
82 Alternatively, use `-z` to specify in NUL-terminated format, without
85 update SP <ref> NUL <new-oid> NUL [<old-oid>] NUL
86 create SP <ref> NUL <new-oid> NUL
87 delete SP <ref> NUL [<old-oid>] NUL
88 verify SP <ref> NUL [<old-oid>] NUL
95 In this format, use 40 "0" to specify a zero value, and use the empty
96 string to specify a missing value.
98 In either format, values can be specified in any form that Git
99 recognizes as an object name. Commands in any other format or a
100 repeated <ref> produce an error. Command meanings are:
103 Set <ref> to <new-oid> after verifying <old-oid>, if given.
104 Specify a zero <new-oid> to ensure the ref does not exist
105 after the update and/or a zero <old-oid> to make sure the
106 ref does not exist before the update.
109 Create <ref> with <new-oid> after verifying it does not
110 exist. The given <new-oid> may not be zero.
113 Delete <ref> after verifying it exists with <old-oid>, if
114 given. If given, <old-oid> may not be zero.
117 Verify <ref> against <old-oid> but do not change it. If
118 <old-oid> is zero or missing, the ref must not exist.
121 Modify the behavior of the next command naming a <ref>.
122 The only valid option is `no-deref` to avoid dereferencing
126 Start a transaction. In contrast to a non-transactional session, a
127 transaction will automatically abort if the session ends without an
128 explicit commit. This command may create a new empty transaction when
129 the current one has been committed or aborted already.
132 Prepare to commit the transaction. This will create lock files for all
133 queued reference updates. If one reference could not be locked, the
134 transaction will be aborted.
137 Commit all reference updates queued for the transaction, ending the
141 Abort the transaction, releasing all locks if the transaction is in
144 If all <ref>s can be locked with matching <old-oid>s
145 simultaneously, all modifications are performed. Otherwise, no
146 modifications are performed. Note that while each individual
147 <ref> is updated or deleted atomically, a concurrent reader may
148 still see a subset of the modifications.
152 If config parameter "core.logAllRefUpdates" is true and the ref is one
153 under "refs/heads/", "refs/remotes/", "refs/notes/", or a pseudoref
154 like HEAD or ORIG_HEAD; or the file "$GIT_DIR/logs/<ref>" exists then
155 `git update-ref` will append a line to the log file
156 "$GIT_DIR/logs/<ref>" (dereferencing all symbolic refs before creating
157 the log name) describing the change in ref value. Log lines are
160 oldsha1 SP newsha1 SP committer LF
162 Where "oldsha1" is the 40 character hexadecimal value previously
163 stored in <ref>, "newsha1" is the 40 character hexadecimal value of
164 <new-oid> and "committer" is the committer's name, email address
165 and date in the standard Git committer ident format.
169 oldsha1 SP newsha1 SP committer TAB message LF
171 Where all fields are as described above and "message" is the
172 value supplied to the -m option.
174 An update will fail (without changing <ref>) if the current user is
175 unable to create a new log file, append to the existing log file
176 or does not have committer information available.
180 Part of the linkgit:git[1] suite