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>] <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>. 24 25It also allows a "ref" file to be a symbolic pointer to another 26ref file by starting with the four-byte header sequence of 27"ref:". 28 29More importantly, it allows the update of a ref file to follow 30these symbolic pointers, whether they are symlinks or these 31"regular file symbolic refs". It follows *real* symlinks only 32if they start with "refs/": otherwise it will just try to read 33them and update them as a regular file (i.e. it will allow the 34filesystem to follow them, but will overwrite such a symlink to 35somewhere else with a regular filename). 36 37In general, using 38 39 git-update-ref HEAD "$head" 40 41should be a _lot_ safer than doing 42 43 echo "$head" > "$GIT_DIR/HEAD" 44 45both from a symlink following standpoint *and* an error checking 46standpoint. The "refs/" rule for symlinks means that symlinks 47that point to "outside" the tree are safe: they'll be followed 48for reading but not for writing (so we'll never write through a 49ref symlink to some other tree, if you have copied a whole 50archive by creating a symlink tree). 51 52Logging Updates 53--------------- 54If config parameter "core.logAllRefUpdates" is true or the file 55"$GIT_DIR/logs/<ref>" exists then `git-update-ref` will append 56a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all 57symbolic refs before creating the log name) describing the change 58in ref value. Log lines are formatted as: 59 60 . oldsha1 SP newsha1 SP committer LF 61+ 62Where "oldsha1" is the 40 character hexadecimal value previously 63stored in <ref>, "newsha1" is the 40 character hexadecimal value of 64<newvalue> and "committer" is the committer's name, email address 65and date in the standard GIT committer ident format. 66 67Optionally with -m: 68 69 . oldsha1 SP newsha1 SP committer TAB message LF 70+ 71Where all fields are as described above and "message" is the 72value supplied to the -m option. 73 74An update will fail (without changing <ref>) if the current user is 75unable to create a new log file, append to the existing log file 76or does not have committer information available. 77 78Author 79------ 80Written by Linus Torvalds <torvalds@osdl.org>. 81 82GIT 83--- 84Part of the gitlink:git[7] suite