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' [-p] [-r] [-z] [-m] [-M] [-R] [--cached] <tree-ish>
  13
  14 DESCRIPTION
  15 -----------
  16 Compares the content and mode of the blobs found via a tree object
  17 with the content of the current cache and, optionally ignoring the
  18 stat state of the file on disk.
  19
  20 OPTIONS
  21 -------
  22 <tree-ish>::
  23         The id of a tree object to diff against.
  24
  25 -p::
  26         Generate patch (see section on generating patches)
  27
  28 -r::
  29         This flag does not mean anything.  It is there only to match
  30         "git-diff-tree".  Unlike "git-diff-tree", "git-diff-cache"
  31         always looks at all the subdirectories.
  32
  33 -z::
  34         \0 line termination on output
  35
  36 -M::
  37         Detect renames; implies -p.
  38
  39 -R::
  40         Output diff in reverse.
  41
  42 --cached::
  43         do not consider the on-disk file at all
  44
  45 -m::
  46         By default, files recorded in the index but not checked
  47         out are reported as deleted.  This flag makes
  48         "git-diff-cache" say that all non-checked-out files are up
  49         to date.
  50
  51 Output format
  52 -------------
  53 include::diff-format.txt[]
  54
  55 Operating Modes
  56 ---------------
  57 You can choose whether you want to trust the index file entirely
  58 (using the '--cached' flag) or ask the diff logic to show any files
  59 that don't match the stat state as being "tentatively changed".  Both
  60 of these operations are very useful indeed.
  61
  62 Cached Mode
  63 -----------
  64 If '--cached' is specified, it allows you to ask:
  65
  66         show me the differences between HEAD and the current index
  67         contents (the ones I'd write with a "git-write-tree")
  68
  69 For example, let's say that you have worked on your index file, and are
  70 ready to commit. You want to see eactly *what* you are going to commit is
  71 without having to write a new tree object and compare it that way, and to
  72 do that, you just do
  73
  74         git-diff-cache --cached $(cat .git/HEAD)
  75
  76 Example: let's say I had renamed `commit.c` to `git-commit.c`, and I had
  77 done an "git-update-cache" to make that effective in the index file.
  78 "git-diff-files" wouldn't show anything at all, since the index file
  79 matches my working directory. But doing a "git-diff-cache" does:
  80
  81   torvalds@ppc970:~/git> git-diff-cache --cached $(cat .git/HEAD)
  82   -100644 blob    4161aecc6700a2eb579e842af0b7f22b98443f74        commit.c
  83   +100644 blob    4161aecc6700a2eb579e842af0b7f22b98443f74        git-commit.c
  84
  85 You can trivially see that the above is a rename.
  86
  87 In fact, "git-diff-cache --cached" *should* always be entirely equivalent to
  88 actually doing a "git-write-tree" and comparing that. Except this one is much
  89 nicer for the case where you just want to check where you are.
  90
  91 So doing a "git-diff-cache --cached" is basically very useful when you are
  92 asking yourself "what have I already marked for being committed, and
  93 what's the difference to a previous tree".
  94
  95 Non-cached Mode
  96 ---------------
  97 The "non-cached" mode takes a different approach, and is potentially
  98 the more useful of the two in that what it does can't be emulated with
  99 a "git-write-tree" + "git-diff-tree". Thus that's the default mode.
 100 The non-cached version asks the question:
 101
 102    show me the differences between HEAD and the currently checked out
 103    tree - index contents _and_ files that aren't up-to-date
 104
 105 which is obviously a very useful question too, since that tells you what
 106 you *could* commit. Again, the output matches the "git-diff-tree -r"
 107 output to a tee, but with a twist.
 108
 109 The twist is that if some file doesn't match the cache, we don't have
 110 a backing store thing for it, and we use the magic "all-zero" sha1 to
 111 show that. So let's say that you have edited `kernel/sched.c`, but
 112 have not actually done a "git-update-cache" on it yet - there is no
 113 "object" associated with the new state, and you get:
 114
 115   torvalds@ppc970:~/v2.6/linux> git-diff-cache $(cat .git/HEAD )
 116   *100644->100664 blob    7476bb......->000000......      kernel/sched.c
 117
 118 ie it shows that the tree has changed, and that `kernel/sched.c` has is
 119 not up-to-date and may contain new stuff. The all-zero sha1 means that to
 120 get the real diff, you need to look at the object in the working directory
 121 directly rather than do an object-to-object diff.
 122
 123 NOTE! As with other commands of this type, "git-diff-cache" does not
 124 actually look at the contents of the file at all. So maybe
 125 `kernel/sched.c` hasn't actually changed, and it's just that you
 126 touched it. In either case, it's a note that you need to
 127 "git-upate-cache" it to make the cache be in sync.
 128
 129 NOTE 2! You can have a mixture of files show up as "has been updated"
 130 and "is still dirty in the working directory" together. You can always
 131 tell which file is in which state, since the "has been updated" ones
 132 show a valid sha1, and the "not in sync with the index" ones will
 133 always have the special all-zero sha1.
 134
 135
 136 Author
 137 ------
 138 Written by Linus Torvalds <torvalds@osdl.org>
 139
 140 Documentation
 141 --------------
 142 Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
 143
 144 GIT
 145 ---
 146 Part of the link:git.html[git] suite
 147