1git-update-ref(1) 2================= 3 4NAME 5---- 6git-update-ref - Update the object name stored in a ref safely 7 8SYNOPSIS 9-------- 10'git update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>]) 11 12DESCRIPTION 13----------- 14Given two arguments, stores the <newvalue> in the <ref>, possibly 15dereferencing the symbolic refs. E.g. `git update-ref HEAD 16<newvalue>` updates the current branch head to the new object. 17 18Given three arguments, stores the <newvalue> in the <ref>, 19possibly dereferencing the symbolic refs, after verifying that 20the current value of the <ref> matches <oldvalue>. 21E.g. `git update-ref refs/heads/master <newvalue> <oldvalue>` 22updates the master branch head to <newvalue> only if its current 23value is <oldvalue>. You can specify 40 "0" or an empty string 24as <oldvalue> to make sure that the ref you are creating does 25not exist. 26 27It also allows a "ref" file to be a symbolic pointer to another 28ref file by starting with the four-byte header sequence of 29"ref:". 30 31More importantly, it allows the update of a ref file to follow 32these symbolic pointers, whether they are symlinks or these 33"regular file symbolic refs". It follows *real* symlinks only 34if they start with "refs/": otherwise it will just try to read 35them and update them as a regular file (i.e. it will allow the 36filesystem to follow them, but will overwrite such a symlink to 37somewhere else with a regular filename). 38 39If --no-deref is given, <ref> itself is overwritten, rather than 40the result of following the symbolic pointers. 41 42In general, using 43 44 git update-ref HEAD "$head" 45 46should be a _lot_ safer than doing 47 48 echo "$head" > "$GIT_DIR/HEAD" 49 50both from a symlink following standpoint *and* an error checking 51standpoint. The "refs/" rule for symlinks means that symlinks 52that point to "outside" the tree are safe: they'll be followed 53for reading but not for writing (so we'll never write through a 54ref symlink to some other tree, if you have copied a whole 55archive by creating a symlink tree). 56 57With `-d` flag, it deletes the named <ref> after verifying it 58still contains <oldvalue>. 59 60 61Logging Updates 62--------------- 63If config parameter "core.logAllRefUpdates" is true or the file 64"$GIT_DIR/logs/<ref>" exists then `git update-ref` will append 65a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all 66symbolic refs before creating the log name) describing the change 67in ref value. Log lines are formatted as: 68 69 . oldsha1 SP newsha1 SP committer LF 70+ 71Where "oldsha1" is the 40 character hexadecimal value previously 72stored in <ref>, "newsha1" is the 40 character hexadecimal value of 73<newvalue> and "committer" is the committer's name, email address 74and date in the standard GIT committer ident format. 75 76Optionally with -m: 77 78 . oldsha1 SP newsha1 SP committer TAB message LF 79+ 80Where all fields are as described above and "message" is the 81value supplied to the -m option. 82 83An update will fail (without changing <ref>) if the current user is 84unable to create a new log file, append to the existing log file 85or does not have committer information available. 86 87Author 88------ 89Written by Linus Torvalds <torvalds@osdl.org>. 90 91GIT 92--- 93Part of the linkgit:git[1] suite