1git-update-ref(1) 2================= 3 4NAME 5---- 6git-update-ref - Update the object name stored in a ref safely 7 8SYNOPSIS 9-------- 10[verse] 11'git update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>]) 12 13DESCRIPTION 14----------- 15Given two arguments, stores the <newvalue> in the <ref>, possibly 16dereferencing the symbolic refs. E.g. `git update-ref HEAD 17<newvalue>` updates the current branch head to the new object. 18 19Given three arguments, stores the <newvalue> in the <ref>, 20possibly dereferencing the symbolic refs, after verifying that 21the current value of the <ref> matches <oldvalue>. 22E.g. `git update-ref refs/heads/master <newvalue> <oldvalue>` 23updates the master branch head to <newvalue> only if its current 24value is <oldvalue>. You can specify 40 "0" or an empty string 25as <oldvalue> to make sure that the ref you are creating does 26not exist. 27 28It also allows a "ref" file to be a symbolic pointer to another 29ref file by starting with the four-byte header sequence of 30"ref:". 31 32More importantly, it allows the update of a ref file to follow 33these symbolic pointers, whether they are symlinks or these 34"regular file symbolic refs". It follows *real* symlinks only 35if they start with "refs/": otherwise it will just try to read 36them and update them as a regular file (i.e. it will allow the 37filesystem to follow them, but will overwrite such a symlink to 38somewhere else with a regular filename). 39 40If --no-deref is given, <ref> itself is overwritten, rather than 41the result of following the symbolic pointers. 42 43In general, using 44 45 git update-ref HEAD "$head" 46 47should be a _lot_ safer than doing 48 49 echo "$head" > "$GIT_DIR/HEAD" 50 51both from a symlink following standpoint *and* an error checking 52standpoint. The "refs/" rule for symlinks means that symlinks 53that point to "outside" the tree are safe: they'll be followed 54for reading but not for writing (so we'll never write through a 55ref symlink to some other tree, if you have copied a whole 56archive by creating a symlink tree). 57 58With `-d` flag, it deletes the named <ref> after verifying it 59still contains <oldvalue>. 60 61 62Logging Updates 63--------------- 64If config parameter "core.logAllRefUpdates" is true and the ref is one under 65"refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic ref HEAD; or 66the file "$GIT_DIR/logs/<ref>" exists then `git update-ref` will append 67a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all 68symbolic refs before creating the log name) describing the change 69in ref value. Log lines are formatted as: 70 71 . oldsha1 SP newsha1 SP committer LF 72+ 73Where "oldsha1" is the 40 character hexadecimal value previously 74stored in <ref>, "newsha1" is the 40 character hexadecimal value of 75<newvalue> and "committer" is the committer's name, email address 76and date in the standard Git committer ident format. 77 78Optionally with -m: 79 80 . oldsha1 SP newsha1 SP committer TAB message LF 81+ 82Where all fields are as described above and "message" is the 83value supplied to the -m option. 84 85An update will fail (without changing <ref>) if the current user is 86unable to create a new log file, append to the existing log file 87or does not have committer information available. 88 89GIT 90--- 91Part of the linkgit:git[1] suite