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