Documentation/git-diff-cache.txt

   1 git-diff-cache(1)
   2 =================
   3 v0.1, May 2005
   4
   5 NAME
   6 ----
   7 git-diff-cache - Compares content and mode of blobs between the cache and repository
   8
   9
  10 SYNOPSIS
  11 --------
  12 'git-diff-cache' [-m] [--cached] [<common diff options>] <tree-ish> [<path>...]
  13
  14 DESCRIPTION
  15 -----------
  16 Compares the content and mode of the blobs found via a tree
  17 object with the content of the current cache and, optionally
  18 ignoring the stat state of the file on disk.  When paths are
  19 specified, compares only those named paths.  Otherwise all
  20 entries in the cache are compared.
  21
  22 OPTIONS
  23 -------
  24 include::diff-options.txt[]
  25
  26 <tree-ish>::
  27         The id of a tree object to diff against.
  28
  29 --cached::
  30         do not consider the on-disk file at all
  31
  32 -m::
  33         By default, files recorded in the index but not checked
  34         out are reported as deleted.  This flag makes
  35         "git-diff-cache" say that all non-checked-out files are up
  36         to date.
  37
  38 Output format
  39 -------------
  40 include::diff-format.txt[]
  41
  42 Operating Modes
  43 ---------------
  44 You can choose whether you want to trust the index file entirely
  45 (using the '--cached' flag) or ask the diff logic to show any files
  46 that don't match the stat state as being "tentatively changed".  Both
  47 of these operations are very useful indeed.
  48
  49 Cached Mode
  50 -----------
  51 If '--cached' is specified, it allows you to ask:
  52
  53         show me the differences between HEAD and the current index
  54         contents (the ones I'd write with a "git-write-tree")
  55
  56 For example, let's say that you have worked on your index file, and are
  57 ready to commit. You want to see eactly *what* you are going to commit is
  58 without having to write a new tree object and compare it that way, and to
  59 do that, you just do
  60
  61         git-diff-cache --cached $(cat .git/HEAD)
  62
  63 Example: let's say I had renamed `commit.c` to `git-commit.c`, and I had
  64 done an "git-update-cache" to make that effective in the index file.
  65 "git-diff-files" wouldn't show anything at all, since the index file
  66 matches my working directory. But doing a "git-diff-cache" does:
  67
  68   torvalds@ppc970:~/git> git-diff-cache --cached $(cat .git/HEAD)
  69   -100644 blob    4161aecc6700a2eb579e842af0b7f22b98443f74        commit.c
  70   +100644 blob    4161aecc6700a2eb579e842af0b7f22b98443f74        git-commit.c
  71
  72 You can trivially see that the above is a rename.
  73
  74 In fact, "git-diff-cache --cached" *should* always be entirely equivalent to
  75 actually doing a "git-write-tree" and comparing that. Except this one is much
  76 nicer for the case where you just want to check where you are.
  77
  78 So doing a "git-diff-cache --cached" is basically very useful when you are
  79 asking yourself "what have I already marked for being committed, and
  80 what's the difference to a previous tree".
  81
  82 Non-cached Mode
  83 ---------------
  84 The "non-cached" mode takes a different approach, and is potentially
  85 the more useful of the two in that what it does can't be emulated with
  86 a "git-write-tree" + "git-diff-tree". Thus that's the default mode.
  87 The non-cached version asks the question:
  88
  89    show me the differences between HEAD and the currently checked out
  90    tree - index contents _and_ files that aren't up-to-date
  91
  92 which is obviously a very useful question too, since that tells you what
  93 you *could* commit. Again, the output matches the "git-diff-tree -r"
  94 output to a tee, but with a twist.
  95
  96 The twist is that if some file doesn't match the cache, we don't have
  97 a backing store thing for it, and we use the magic "all-zero" sha1 to
  98 show that. So let's say that you have edited `kernel/sched.c`, but
  99 have not actually done a "git-update-cache" on it yet - there is no
 100 "object" associated with the new state, and you get:
 101
 102   torvalds@ppc970:~/v2.6/linux> git-diff-cache $(cat .git/HEAD )
 103   *100644->100664 blob    7476bb......->000000......      kernel/sched.c
 104
 105 ie it shows that the tree has changed, and that `kernel/sched.c` has is
 106 not up-to-date and may contain new stuff. The all-zero sha1 means that to
 107 get the real diff, you need to look at the object in the working directory
 108 directly rather than do an object-to-object diff.
 109
 110 NOTE! As with other commands of this type, "git-diff-cache" does not
 111 actually look at the contents of the file at all. So maybe
 112 `kernel/sched.c` hasn't actually changed, and it's just that you
 113 touched it. In either case, it's a note that you need to
 114 "git-upate-cache" it to make the cache be in sync.
 115
 116 NOTE 2! You can have a mixture of files show up as "has been updated"
 117 and "is still dirty in the working directory" together. You can always
 118 tell which file is in which state, since the "has been updated" ones
 119 show a valid sha1, and the "not in sync with the index" ones will
 120 always have the special all-zero sha1.
 121
 122
 123 Author
 124 ------
 125 Written by Linus Torvalds <torvalds@osdl.org>
 126
 127 Documentation
 128 --------------
 129 Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
 130
 131 GIT
 132 ---
 133 Part of the link:git.html[git] suite
 134