1GIT-UPDATE-REF(1) Git Manual GIT-UPDATE-REF(1)
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6 git-update-ref - Update the object name stored in a ref safely
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9 git update-ref [-m <reason>] [--no-deref] (-d <ref> [<oldvalue>] | [--create-reflog] <ref> <newvalue> [<oldvalue>] | --stdin [-z])
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12 Given two arguments, stores the <newvalue> in the <ref>, possibly
13 dereferencing the symbolic refs. E.g. git update-ref HEAD <newvalue>
14 updates the current branch head to the new object.
15 Given three arguments, stores the <newvalue> in the <ref>, possibly
17 dereferencing the symbolic refs, after verifying that the current value
18 of the <ref> matches <oldvalue>. E.g. git update-ref refs/heads/master
19 <newvalue> <oldvalue> updates the master branch head to <newvalue> only
20 if its current value is <oldvalue>. You can specify 40 "0" or an empty
21 string as <oldvalue> to make sure that the ref you are creating does
22 not exist.
23 It also allows a "ref" file to be a symbolic pointer to another ref
25 file by starting with the four-byte header sequence of "ref:".
26 More importantly, it allows the update of a ref file to follow these
28 symbolic pointers, whether they are symlinks or these "regular file
29 symbolic refs". It follows real symlinks only if they start with
30 "refs/": otherwise it will just try to read them and update them as a
31 regular file (i.e. it will allow the filesystem to follow them, but
32 will overwrite such a symlink to somewhere else with a regular
33 filename).
34 If --no-deref is given, <ref> itself is overwritten, rather than the
36 result of following the symbolic pointers.
37 In general, using
39 git update-ref HEAD "$head"
41 should be a lot safer than doing
43 echo "$head" > "$GIT_DIR/HEAD"
45 both from a symlink following standpoint and an error checking
47 standpoint. The "refs/" rule for symlinks means that symlinks that
48 point to "outside" the tree are safe: they’ll be followed for reading
49 but not for writing (so we’ll never write through a ref symlink to some
50 other tree, if you have copied a whole archive by creating a symlink
51 tree).
52 With -d flag, it deletes the named <ref> after verifying it still
54 contains <oldvalue>.
55 With --stdin, update-ref reads instructions from standard input and
57 performs all modifications together. Specify commands of the form:
58 update SP <ref> SP <newvalue> [SP <oldvalue>] LF
60 create SP <ref> SP <newvalue> LF
61 delete SP <ref> [SP <oldvalue>] LF
62 verify SP <ref> [SP <oldvalue>] LF
63 option SP <opt> LF
64 With --create-reflog, update-ref will create a reflog for each ref even
66 if one would not ordinarily be created.
67 Quote fields containing whitespace as if they were strings in C source
69 code; i.e., surrounded by double-quotes and with backslash escapes. Use
70 40 "0" characters or the empty string to specify a zero value. To
71 specify a missing value, omit the value and its preceding SP entirely.
72 Alternatively, use -z to specify in NUL-terminated format, without
74 quoting:
75 update SP <ref> NUL <newvalue> NUL [<oldvalue>] NUL
77 create SP <ref> NUL <newvalue> NUL
78 delete SP <ref> NUL [<oldvalue>] NUL
79 verify SP <ref> NUL [<oldvalue>] NUL
80 option SP <opt> NUL
81 In this format, use 40 "0" to specify a zero value, and use the empty
83 string to specify a missing value.
84 In either format, values can be specified in any form that Git
86 recognizes as an object name. Commands in any other format or a
87 repeated <ref> produce an error. Command meanings are:
88 update
90 Set <ref> to <newvalue> after verifying <oldvalue>, if given.
91 Specify a zero <newvalue> to ensure the ref does not exist after
92 the update and/or a zero <oldvalue> to make sure the ref does not
93 exist before the update.
94 create
96 Create <ref> with <newvalue> after verifying it does not exist. The
97 given <newvalue> may not be zero.
98 delete
100 Delete <ref> after verifying it exists with <oldvalue>, if given.
101 If given, <oldvalue> may not be zero.
102 verify
104 Verify <ref> against <oldvalue> but do not change it. If <oldvalue>
105 zero or missing, the ref must not exist.
106 option
108 Modify behavior of the next command naming a <ref>. The only valid
109 option is no-deref to avoid dereferencing a symbolic ref.
110 If all <ref>s can be locked with matching <oldvalue>s simultaneously,
112 all modifications are performed. Otherwise, no modifications are
113 performed. Note that while each individual <ref> is updated or deleted
114 atomically, a concurrent reader may still see a subset of the
115 modifications.
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118 If config parameter "core.logAllRefUpdates" is true and the ref is one
119 under "refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic
120 ref HEAD; or the file "$GIT_DIR/logs/<ref>" exists then git update-ref
121 will append a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing
122 all symbolic refs before creating the log name) describing the change
123 in ref value. Log lines are formatted as:
124 oldsha1 SP newsha1 SP committer LF
126 Where "oldsha1" is the 40 character hexadecimal value previously stored
128 in <ref>, "newsha1" is the 40 character hexadecimal value of <newvalue>
129 and "committer" is the committer’s name, email address and date in the
130 standard Git committer ident format.
131 Optionally with -m:
133 oldsha1 SP newsha1 SP committer TAB message LF
135 Where all fields are as described above and "message" is the value
137 supplied to the -m option.
138 An update will fail (without changing <ref>) if the current user is
140 unable to create a new log file, append to the existing log file or
141 does not have committer information available.
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144 Part of the git(1) suite
145Git 2.26.2 2020-04-20 GIT-UPDATE-REF(1)