1GIT-UPDATE-REF(1)                 Git Manual                 GIT-UPDATE-REF(1)
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NAME

6       git-update-ref - Update the object name stored in a ref safely
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SYNOPSIS

9       git update-ref [-m <reason>] [--no-deref] (-d <ref> [<oldvalue>] | [--create-reflog] <ref> <newvalue> [<oldvalue>] | --stdin [-z])
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DESCRIPTION

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

119       If config parameter "core.logAllRefUpdates" is true and the ref is one
120       under "refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic
121       ref HEAD; or the file "$GIT_DIR/logs/<ref>" exists then git update-ref
122       will append a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing
123       all symbolic refs before creating the log name) describing the change
124       in ref value. Log lines are formatted as:
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126           oldsha1 SP newsha1 SP committer LF
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128       Where "oldsha1" is the 40 character hexadecimal value previously stored
129       in <ref>, "newsha1" is the 40 character hexadecimal value of <newvalue>
130       and "committer" is the committer’s name, email address and date in the
131       standard Git committer ident format.
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133       Optionally with -m:
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135           oldsha1 SP newsha1 SP committer TAB message LF
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137       Where all fields are as described above and "message" is the value
138       supplied to the -m option.
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140       An update will fail (without changing <ref>) if the current user is
141       unable to create a new log file, append to the existing log file or
142       does not have committer information available.
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GIT

145       Part of the git(1) suite
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149Git 2.24.1                        12/10/2019                 GIT-UPDATE-REF(1)
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