Documentation / git-update-ref.txton commit Add callback data to for_each_ref() family. (cb5d709)
   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