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` <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 52Author 53------ 54Written by Linus Torvalds <torvalds@osdl.org>. 55 56GIT 57--- 58Part of the gitlink:git[7] suite