git-diff-cache(1) Manual Page

NAME

git - diff-cache - Compares content and mode of blobs between the cache and repository

SYNOPSIS

git-diff-cache [-p] [-r] [-z] [-m] [-B] [-M] [-R] [-C] [-O<orderfile>] [-S<string>] [—pickaxe-all] [—cached] <tree-ish> [<path>…]

DESCRIPTION

Compares the content and mode of the blobs found via a tree object with the content of the current cache and, optionally ignoring the stat state of the file on disk. When paths are specified, compares only those named paths. Otherwise all entries in the cache are compared.

OPTIONS

<tree-ish>
The id of a tree object to diff against.
-p
Generate patch (see section on generating patches)
-r
This flag does not mean anything. It is there only to match "git-diff-tree". Unlike "git-diff-tree", "git-diff-cache" always looks at all the subdirectories.
-z
\0 line termination on output
-B
Break complete rewrite changes into pairs of delete and create.
-M
Detect renames.
-C
Detect copies as well as renames.
-S<string>
Look for differences that contains the change in <string>.
—pickaxe-all
When -S finds a change, show all the changes in that changeset, not just the files that contains the change in <string>.
-O<orderfile>
Output the patch in the order specified in the <orderfile>, which has one shell glob pattern per line.
-R
Swap two inputs; that is, show differences from cache or on-disk file to tree contents.
—cached
do not consider the on-disk file at all
-m
By default, files recorded in the index but not checked out are reported as deleted. This flag makes "git-diff-cache" say that all non-checked-out files are up to date.

Output format

The output format from "git-diff-cache", "git-diff-tree" and "git-diff-files" is very similar.

These commands all compare two sets of things; what are compared are different:

git-diff-cache <tree-ish>
compares the <tree-ish> and the files on the filesystem.
git-diff-cache —cached <tree-ish>
compares the <tree-ish> and the cache.
git-diff-tree [-r] <tree-ish-1> <tree-ish-2> [<pattern>…]
compares the trees named by the two arguments.
git-diff-files [<pattern>…]
compares the cache and the files on the filesystem.

An output line is formatted this way:

in-place edit :100644 100644 bcd1234… 0123456… M file0 copy-edit :100644 100644 abcd123… 1234567… C68 file1 file2 rename-edit :100644 100644 abcd123… 1234567… R86 file1 file3 create :000000 100644 0000000… 1234567… N file4 delete :100644 000000 1234567… 0000000… D file5 unmerged :000000 000000 0000000… 0000000… U file6

That is, from the left to the right:

 (1) a colon.
 (2) mode for "src"; 000000 if creation or unmerged.
 (3) a space.
 (4) mode for "dst"; 000000 if deletion or unmerged.
 (5) a space.
 (6) sha1 for "src"; 0{40} if creation or unmerged.
 (7) a space.
 (8) sha1 for "dst"; 0{40} if creation, unmerged or "look at work tree".
 (9) a space.
(10) status, followed by optional "score" number.
(11) a tab or a NUL when '-z' option is used.
(12) path for "src"
(13) a tab or a NUL when '-z' option is used; only exists for C or R.
(14) path for "dst"; only exists for C or R.
(15) an LF or a NUL when '-z' option is used, to terminate the record.

<sha1> is shown as all 0's if new is a file on the filesystem and it is out of sync with the cache. Example:

:100644 100644 5be4a4...... 000000...... M file.c

Generating patches with -p

When "git-diff-cache", "git-diff-tree", or "git-diff-files" are run with a -p option, they do not produce the output described above; instead they produce a patch file.

The patch generation can be customized at two levels. This customization also applies to "git-diff-helper".

  1. When the environment variable GIT_EXTERNAL_DIFF is not set, these commands internally invoke "diff" like this:

    diff -L a/<path> -L a/<path> -pu <old> <new>
    

    For added files, /dev/null is used for <old>. For removed files, /dev/null is used for <new>

    The "diff" formatting options can be customized via the environment variable GIT_DIFF_OPTS. For example, if you prefer context diff:

    GIT_DIFF_OPTS=-c git-diff-cache -p $(cat .git/HEAD)
    
  2. When the environment variable GIT_EXTERNAL_DIFF is set, the program named by it is called, instead of the diff invocation described above.

    For a path that is added, removed, or modified, GIT_EXTERNAL_DIFF is called with 7 parameters:

    path old-file old-hex old-mode new-file new-hex new-mode
    

    where:

    <old|new>-file are files GIT_EXTERNAL_DIFF can use to read the contents of <old|ne>,
    <old|new>-hex are the 40-hexdigit SHA1 hashes,
    <old|new>-mode are the octal representation of the file modes.

    The file parameters can point at the user's working file (e.g. new-file in "git-diff-files"), /dev/null (e.g. old-file when a new file is added), or a temporary file (e.g. old-file in the cache). GIT_EXTERNAL_DIFF should not worry about unlinking the temporary file --- it is removed when GIT_EXTERNAL_DIFF exits.

For a path that is unmerged, GIT_EXTERNAL_DIFF is called with 1 parameter, <path>.

Git specific extention to diff format

What -p option produces is slightly different from the traditional diff format.

(1) It is preceeded with a "git diff" header, that looks like
    this:
diff --git a/file1 b/file2
The a/ and b/ filenames are the same unless rename/copy is
involved.  Especially, even for a creation or a deletion,
/dev/null is _not_ used in place of a/ or b/ filename.
When rename/copy is involved, file1 and file2 shows the
name of the source file of the rename/copy and the name of
the file that rename/copy produces, respectively.
(2) It is followed by extended header lines that are one or
    more of:
old mode <mode>
new mode <mode>
deleted file mode <mode>
new file mode <mode>
copy from <path>
copy to <path>
rename from <path>
rename to <path>
similarity index <number>
dissimilarity index <number>

Operating Modes

You can choose whether you want to trust the index file entirely (using the —cached flag) or ask the diff logic to show any files that don't match the stat state as being "tentatively changed". Both of these operations are very useful indeed.

Cached Mode

If —cached is specified, it allows you to ask:

show me the differences between HEAD and the current index
contents (the ones I'd write with a "git-write-tree")

For example, let's say that you have worked on your index file, and are ready to commit. You want to see eactly what you are going to commit is without having to write a new tree object and compare it that way, and to do that, you just do

git-diff-cache --cached $(cat .git/HEAD)

Example: let's say I had renamed commit.c to git-commit.c, and I had done an "git-update-cache" to make that effective in the index file. "git-diff-files" wouldn't show anything at all, since the index file matches my working directory. But doing a "git-diff-cache" does:

torvalds@ppc970:~/git> git-diff-cache --cached $(cat .git/HEAD)
-100644 blob    4161aecc6700a2eb579e842af0b7f22b98443f74        commit.c
+100644 blob    4161aecc6700a2eb579e842af0b7f22b98443f74        git-commit.c

You can trivially see that the above is a rename.

In fact, "git-diff-cache —cached" should always be entirely equivalent to actually doing a "git-write-tree" and comparing that. Except this one is much nicer for the case where you just want to check where you are.

So doing a "git-diff-cache —cached" is basically very useful when you are asking yourself "what have I already marked for being committed, and what's the difference to a previous tree".

Non-cached Mode

The "non-cached" mode takes a different approach, and is potentially the more useful of the two in that what it does can't be emulated with a "git-write-tree" + "git-diff-tree". Thus that's the default mode. The non-cached version asks the question:

show me the differences between HEAD and the currently checked out
tree - index contents _and_ files that aren't up-to-date

which is obviously a very useful question too, since that tells you what you could commit. Again, the output matches the "git-diff-tree -r" output to a tee, but with a twist.

The twist is that if some file doesn't match the cache, we don't have a backing store thing for it, and we use the magic "all-zero" sha1 to show that. So let's say that you have edited kernel/sched.c, but have not actually done a "git-update-cache" on it yet - there is no "object" associated with the new state, and you get:

torvalds@ppc970:~/v2.6/linux> git-diff-cache $(cat .git/HEAD )
*100644->100664 blob    7476bb......->000000......      kernel/sched.c

ie it shows that the tree has changed, and that kernel/sched.c has is not up-to-date and may contain new stuff. The all-zero sha1 means that to get the real diff, you need to look at the object in the working directory directly rather than do an object-to-object diff.

NOTE! As with other commands of this type, "git-diff-cache" does not actually look at the contents of the file at all. So maybe kernel/sched.c hasn't actually changed, and it's just that you touched it. In either case, it's a note that you need to "git-upate-cache" it to make the cache be in sync.

NOTE 2! You can have a mixture of files show up as "has been updated" and "is still dirty in the working directory" together. You can always tell which file is in which state, since the "has been updated" ones show a valid sha1, and the "not in sync with the index" ones will always have the special all-zero sha1.

Author

Written by Linus Torvalds <torvalds@osdl.org>

Documentation

Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.

GIT

Part of the git(7) suite