git-diff-index - Compare a tree to the working tree or index


   git diff-index [-m] [--cached] [<common diff options>] <tree-ish> [<path>...]


   Compares the content and mode of the blobs found in a tree object with
   the corresponding tracked files in the working tree, or with the
   corresponding paths in the index. When <path> arguments are present,
   compares only paths matching those patterns. Otherwise all tracked
   files are compared.


   -p, -u, --patch
       Generate patch (see section on generating patches).

   -s, --no-patch
       Suppress diff output. Useful for commands like git show that show
       the patch by default, or to cancel the effect of --patch.

   -U<n>, --unified=<n>
       Generate diffs with <n> lines of context instead of the usual
       three. Implies -p.

       Generate the diff in raw format. This is the default.

       Synonym for -p --raw.

   --compaction-heuristic, --no-compaction-heuristic
       These are to help debugging and tuning an experimental heuristic
       (which is off by default) that shifts the hunk boundary in an
       attempt to make the resulting patch easier to read.

       Spend extra time to make sure the smallest possible diff is

       Generate a diff using the "patience diff" algorithm.

       Generate a diff using the "histogram diff" algorithm.

       Choose a diff algorithm. The variants are as follows:

       default, myers
           The basic greedy diff algorithm. Currently, this is the

           Spend extra time to make sure the smallest possible diff is

           Use "patience diff" algorithm when generating patches.

           This algorithm extends the patience algorithm to "support
           low-occurrence common elements".

       For instance, if you configured diff.algorithm variable to a
       non-default value and want to use the default one, then you have to
       use --diff-algorithm=default option.

       Generate a diffstat. By default, as much space as necessary will be
       used for the filename part, and the rest for the graph part.
       Maximum width defaults to terminal width, or 80 columns if not
       connected to a terminal, and can be overridden by <width>. The
       width of the filename part can be limited by giving another width
       <name-width> after a comma. The width of the graph part can be
       limited by using --stat-graph-width=<width> (affects all commands
       generating a stat graph) or by setting diff.statGraphWidth=<width>
       (does not affect git format-patch). By giving a third parameter
       <count>, you can limit the output to the first <count> lines,
       followed by ...  if there are more.

       These parameters can also be set individually with
       --stat-width=<width>, --stat-name-width=<name-width> and

       Similar to --stat, but shows number of added and deleted lines in
       decimal notation and pathname without abbreviation, to make it more
       machine friendly. For binary files, outputs two - instead of saying
       0 0.

       Output only the last line of the --stat format containing total
       number of modified files, as well as number of added and deleted

       Output the distribution of relative amount of changes for each
       sub-directory. The behavior of --dirstat can be customized by
       passing it a comma separated list of parameters. The defaults are
       controlled by the diff.dirstat configuration variable (see git-
       config(1)). The following parameters are available:

           Compute the dirstat numbers by counting the lines that have
           been removed from the source, or added to the destination. This
           ignores the amount of pure code movements within a file. In
           other words, rearranging lines in a file is not counted as much
           as other changes. This is the default behavior when no
           parameter is given.

           Compute the dirstat numbers by doing the regular line-based
           diff analysis, and summing the removed/added line counts. (For
           binary files, count 64-byte chunks instead, since binary files
           have no natural concept of lines). This is a more expensive
           --dirstat behavior than the changes behavior, but it does count
           rearranged lines within a file as much as other changes. The
           resulting output is consistent with what you get from the other
           --*stat options.

           Compute the dirstat numbers by counting the number of files
           changed. Each changed file counts equally in the dirstat
           analysis. This is the computationally cheapest --dirstat
           behavior, since it does not have to look at the file contents
           at all.

           Count changes in a child directory for the parent directory as
           well. Note that when using cumulative, the sum of the
           percentages reported may exceed 100%. The default
           (non-cumulative) behavior can be specified with the
           noncumulative parameter.

           An integer parameter specifies a cut-off percent (3% by
           default). Directories contributing less than this percentage of
           the changes are not shown in the output.

       Example: The following will count changed files, while ignoring
       directories with less than 10% of the total amount of changed
       files, and accumulating child directory counts in the parent
       directories: --dirstat=files,10,cumulative.

       Output a condensed summary of extended header information such as
       creations, renames and mode changes.

       Synonym for -p --stat.

       When --raw, --numstat, --name-only or --name-status has been given,
       do not munge pathnames and use NULs as output field terminators.

       Without this option, each pathname output will have TAB, LF, double
       quotes, and backslash characters replaced with \t, \n, \", and \\,
       respectively, and the pathname will be enclosed in double quotes if
       any of those replacements occurred.

       Show only names of changed files.

       Show only names and status of changed files. See the description of
       the --diff-filter option on what the status letters mean.

       Specify how differences in submodules are shown. When --submodule
       or --submodule=log is given, the log format is used. This format
       lists the commits in the range like git-submodule(1) summary does.
       Omitting the --submodule option or specifying --submodule=short,
       uses the short format. This format just shows the names of the
       commits at the beginning and end of the range. Can be tweaked via
       the diff.submodule configuration variable.

       Show colored diff.  --color (i.e. without =<when>) is the same as
       --color=always.  <when> can be one of always, never, or auto.

       Turn off colored diff. It is the same as --color=never.

       Show a word diff, using the <mode> to delimit changed words. By
       default, words are delimited by whitespace; see --word-diff-regex
       below. The <mode> defaults to plain, and must be one of:

           Highlight changed words using only colors. Implies --color.

           Show words as [-removed-] and {+added+}. Makes no attempts to
           escape the delimiters if they appear in the input, so the
           output may be ambiguous.

           Use a special line-based format intended for script
           consumption. Added/removed/unchanged runs are printed in the
           usual unified diff format, starting with a +/-/` ` character at
           the beginning of the line and extending to the end of the line.
           Newlines in the input are represented by a tilde ~ on a line of
           its own.

           Disable word diff again.

       Note that despite the name of the first mode, color is used to
       highlight the changed parts in all modes if enabled.

       Use <regex> to decide what a word is, instead of considering runs
       of non-whitespace to be a word. Also implies --word-diff unless it
       was already enabled.

       Every non-overlapping match of the <regex> is considered a word.
       Anything between these matches is considered whitespace and
       ignored(!) for the purposes of finding differences. You may want to
       append |[^[:space:]] to your regular expression to make sure that
       it matches all non-whitespace characters. A match that contains a
       newline is silently truncated(!) at the newline.

       For example, --word-diff-regex=.  will treat each character as a
       word and, correspondingly, show differences character by character.

       The regex can also be set via a diff driver or configuration
       option, see gitattributes(5) or git-config(1). Giving it explicitly
       overrides any diff driver or configuration setting. Diff drivers
       override configuration settings.

       Equivalent to --word-diff=color plus (if a regex was specified)

       Turn off rename detection, even when the configuration file gives
       the default to do so.

       Warn if changes introduce conflict markers or whitespace errors.
       What are considered whitespace errors is controlled by
       core.whitespace configuration. By default, trailing whitespaces
       (including lines that solely consist of whitespaces) and a space
       character that is immediately followed by a tab character inside
       the initial indent of the line are considered whitespace errors.
       Exits with non-zero status if problems are found. Not compatible
       with --exit-code.

       Highlight whitespace errors on lines specified by <kind> in the
       color specified by color.diff.whitespace. <kind> is a comma
       separated list of old, new, context. When this option is not given,
       only whitespace errors in new lines are highlighted. E.g.
       --ws-error-highlight=new,old highlights whitespace errors on both
       deleted and added lines.  all can be used as a short-hand for

       Instead of the first handful of characters, show the full pre- and
       post-image blob object names on the "index" line when generating
       patch format output.

       In addition to --full-index, output a binary diff that can be
       applied with git-apply.

       Instead of showing the full 40-byte hexadecimal object name in
       diff-raw format output and diff-tree header lines, show only a
       partial prefix. This is independent of the --full-index option
       above, which controls the diff-patch output format. Non default
       number of digits can be specified with --abbrev=<n>.

   -B[<n>][/<m>], --break-rewrites[=[<n>][/<m>]]
       Break complete rewrite changes into pairs of delete and create.
       This serves two purposes:

       It affects the way a change that amounts to a total rewrite of a
       file not as a series of deletion and insertion mixed together with
       a very few lines that happen to match textually as the context, but
       as a single deletion of everything old followed by a single
       insertion of everything new, and the number m controls this aspect
       of the -B option (defaults to 60%).  -B/70% specifies that less
       than 30% of the original should remain in the result for Git to
       consider it a total rewrite (i.e. otherwise the resulting patch
       will be a series of deletion and insertion mixed together with
       context lines).

       When used with -M, a totally-rewritten file is also considered as
       the source of a rename (usually -M only considers a file that
       disappeared as the source of a rename), and the number n controls
       this aspect of the -B option (defaults to 50%).  -B20% specifies
       that a change with addition and deletion compared to 20% or more of
       the file's size are eligible for being picked up as a possible
       source of a rename to another file.

   -M[<n>], --find-renames[=<n>]
       Detect renames. If n is specified, it is a threshold on the
       similarity index (i.e. amount of addition/deletions compared to the
       file's size). For example, -M90% means Git should consider a
       delete/add pair to be a rename if more than 90% of the file hasn't
       changed. Without a % sign, the number is to be read as a fraction,
       with a decimal point before it. I.e., -M5 becomes 0.5, and is thus
       the same as -M50%. Similarly, -M05 is the same as -M5%. To limit
       detection to exact renames, use -M100%. The default similarity
       index is 50%.

   -C[<n>], --find-copies[=<n>]
       Detect copies as well as renames. See also --find-copies-harder. If
       n is specified, it has the same meaning as for -M<n>.

       For performance reasons, by default, -C option finds copies only if
       the original file of the copy was modified in the same changeset.
       This flag makes the command inspect unmodified files as candidates
       for the source of copy. This is a very expensive operation for
       large projects, so use it with caution. Giving more than one -C
       option has the same effect.

   -D, --irreversible-delete
       Omit the preimage for deletes, i.e. print only the header but not
       the diff between the preimage and /dev/null. The resulting patch is
       not meant to be applied with patch or git apply; this is solely for
       people who want to just concentrate on reviewing the text after the
       change. In addition, the output obviously lack enough information
       to apply such a patch in reverse, even manually, hence the name of
       the option.

       When used together with -B, omit also the preimage in the deletion
       part of a delete/create pair.

       The -M and -C options require O(n^2) processing time where n is the
       number of potential rename/copy targets. This option prevents
       rename/copy detection from running if the number of rename/copy
       targets exceeds the specified number.

       Select only files that are Added (A), Copied (C), Deleted (D),
       Modified (M), Renamed (R), have their type (i.e. regular file,
       symlink, submodule, ...) changed (T), are Unmerged (U), are Unknown
       (X), or have had their pairing Broken (B). Any combination of the
       filter characters (including none) can be used. When *
       (All-or-none) is added to the combination, all paths are selected
       if there is any file that matches other criteria in the comparison;
       if there is no file that matches other criteria, nothing is

       Also, these upper-case letters can be downcased to exclude. E.g.
       --diff-filter=ad excludes added and deleted paths.

       Look for differences that change the number of occurrences of the
       specified string (i.e. addition/deletion) in a file. Intended for
       the scripter's use.

       It is useful when you're looking for an exact block of code (like a
       struct), and want to know the history of that block since it first
       came into being: use the feature iteratively to feed the
       interesting block in the preimage back into -S, and keep going
       until you get the very first version of the block.

       Look for differences whose patch text contains added/removed lines
       that match <regex>.

       To illustrate the difference between -S<regex> --pickaxe-regex and
       -G<regex>, consider a commit with the following diff in the same

           +    return !regexec(regexp, two->ptr, 1, &regmatch, 0);
           -    hit = !regexec(regexp, mf2.ptr, 1, &regmatch, 0);

       While git log -G"regexec\(regexp" will show this commit, git log
       -S"regexec\(regexp" --pickaxe-regex will not (because the number of
       occurrences of that string did not change).

       See the pickaxe entry in gitdiffcore(7) for more information.

       When -S or -G finds a change, show all the changes in that
       changeset, not just the files that contain the change in <string>.

       Treat the <string> given to -S as an extended POSIX regular
       expression to match.

       Output the patch in the order specified in the <orderfile>, which
       has one shell glob pattern per line. This overrides the
       diff.orderFile configuration variable (see git-config(1)). To
       cancel diff.orderFile, use -O/dev/null.

       Swap two inputs; that is, show differences from index or on-disk
       file to tree contents.

       When run from a subdirectory of the project, it can be told to
       exclude changes outside the directory and show pathnames relative
       to it with this option. When you are not in a subdirectory (e.g. in
       a bare repository), you can name which subdirectory to make the
       output relative to by giving a <path> as an argument.

   -a, --text
       Treat all files as text.

       Ignore changes in whitespace at EOL.

   -b, --ignore-space-change
       Ignore changes in amount of whitespace. This ignores whitespace at
       line end, and considers all other sequences of one or more
       whitespace characters to be equivalent.

   -w, --ignore-all-space
       Ignore whitespace when comparing lines. This ignores differences
       even if one line has whitespace where the other line has none.

       Ignore changes whose lines are all blank.

       Show the context between diff hunks, up to the specified number of
       lines, thereby fusing hunks that are close to each other.

   -W, --function-context
       Show whole surrounding functions of changes.

       Make the program exit with codes similar to diff(1). That is, it
       exits with 1 if there were differences and 0 means no differences.

       Disable all output of the program. Implies --exit-code.

       Allow an external diff helper to be executed. If you set an
       external diff driver with gitattributes(5), you need to use this
       option with git-log(1) and friends.

       Disallow external diff drivers.

   --textconv, --no-textconv
       Allow (or disallow) external text conversion filters to be run when
       comparing binary files. See gitattributes(5) for details. Because
       textconv filters are typically a one-way conversion, the resulting
       diff is suitable for human consumption, but cannot be applied. For
       this reason, textconv filters are enabled by default only for git-
       diff(1) and git-log(1), but not for git-format-patch(1) or diff
       plumbing commands.

       Ignore changes to submodules in the diff generation. <when> can be
       either "none", "untracked", "dirty" or "all", which is the default.
       Using "none" will consider the submodule modified when it either
       contains untracked or modified files or its HEAD differs from the
       commit recorded in the superproject and can be used to override any
       settings of the ignore option in git-config(1) or gitmodules(5).
       When "untracked" is used submodules are not considered dirty when
       they only contain untracked content (but they are still scanned for
       modified content). Using "dirty" ignores all changes to the work
       tree of submodules, only changes to the commits stored in the
       superproject are shown (this was the behavior until 1.7.0). Using
       "all" hides all changes to submodules.

       Show the given source prefix instead of "a/".

       Show the given destination prefix instead of "b/".

       Do not show any source or destination prefix.

   For more detailed explanation on these common options, see also

       The id of a tree object to diff against.

       do not consider the on-disk file at all

       By default, files recorded in the index but not checked out are
       reported as deleted. This flag makes git diff-index say that all
       non-checked-out files are up to date.


   The raw output format from "git-diff-index", "git-diff-tree",
   "git-diff-files" and "git diff --raw" are very similar.

   These commands all compare two sets of things; what is compared

   git-diff-index <tree-ish>
       compares the <tree-ish> and the files on the filesystem.

   git-diff-index --cached <tree-ish>
       compares the <tree-ish> and the index.

   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 index and the files on the filesystem.

   The "git-diff-tree" command begins its output by printing the hash of
   what is being compared. After that, all the commands print one output
   line per changed file.

   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... A 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.

   Possible status letters are:

   *   A: addition of a file

   *   C: copy of a file into a new one

   *   D: deletion of a file

   *   M: modification of the contents or mode of a file

   *   R: renaming of a file

   *   T: change in the type of the file

   *   U: file is unmerged (you must complete the merge before it can be

   *   X: "unknown" change type (most probably a bug, please report it)

   Status letters C and R are always followed by a score (denoting the
   percentage of similarity between the source and target of the move or
   copy). Status letter M may be followed by a score (denoting the
   percentage of dissimilarity) for file rewrites.

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


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

   When -z option is not used, TAB, LF, and backslash characters in
   pathnames are represented as \t, \n, and \\, respectively.


   "git-diff-tree", "git-diff-files" and "git-diff --raw" can take -c or
   --cc option to generate diff output also for merge commits. The output
   differs from the format described above in the following way:

    1. there is a colon for each parent

    2. there are more "src" modes and "src" sha1

    3. status is concatenated status characters for each parent

    4. no optional "score" number

    5. single path, only for "dst"


       ::100644 100644 100644 fabadb8... cc95eb0... 4866510... MM      describe.c

   Note that combined diff lists only files which were modified from all


   When "git-diff-index", "git-diff-tree", or "git-diff-files" are run
   with a -p option, "git diff" without the --raw option, or "git log"
   with the "-p" option, they do not produce the output described above;
   instead they produce a patch file. You can customize the creation of
   such patches via the GIT_EXTERNAL_DIFF and the GIT_DIFF_OPTS
   environment variables.

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

    1. It is preceded 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 the a/ or b/ filenames.

       When rename/copy is involved, file1 and file2 show 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 one or more extended header lines:

           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>
           index <hash>..<hash> <mode>

       File modes are printed as 6-digit octal numbers including the file
       type and file permission bits.

       Path names in extended headers do not include the a/ and b/

       The similarity index is the percentage of unchanged lines, and the
       dissimilarity index is the percentage of changed lines. It is a
       rounded down integer, followed by a percent sign. The similarity
       index value of 100% is thus reserved for two equal files, while
       100% dissimilarity means that no line from the old file made it
       into the new one.

       The index line includes the SHA-1 checksum before and after the
       change. The <mode> is included if the file mode does not change;
       otherwise, separate lines indicate the old and the new mode.

    3. TAB, LF, double quote and backslash characters in pathnames are
       represented as \t, \n, \" and \\, respectively. If there is need
       for such substitution then the whole pathname is put in double

    4. All the file1 files in the output refer to files before the commit,
       and all the file2 files refer to files after the commit. It is
       incorrect to apply each change to each file sequentially. For
       example, this patch will swap a and b:

           diff --git a/a b/b
           rename from a
           rename to b
           diff --git a/b b/a
           rename from b
           rename to a


   Any diff-generating command can take the -c or --cc option to produce a
   combined diff when showing a merge. This is the default format when
   showing merges with git-diff(1) or git-show(1). Note also that you can
   give the -m option to any of these commands to force generation of
   diffs with individual parents of a merge.

   A combined diff format looks like this:

       diff --combined describe.c
       index fabadb8,cc95eb0..4866510
       --- a/describe.c
       +++ b/describe.c
       @@@ -98,20 -98,12 +98,20 @@@
               return (a_date > b_date) ? -1 : (a_date == b_date) ? 0 : 1;

       - static void describe(char *arg)
        -static void describe(struct commit *cmit, int last_one)
       ++static void describe(char *arg, int last_one)
        +      unsigned char sha1[20];
        +      struct commit *cmit;
               struct commit_list *list;
               static int initialized = 0;
               struct commit_name *n;

        +      if (get_sha1(arg, sha1) < 0)
        +              usage(describe_usage);
        +      cmit = lookup_commit_reference(sha1);
        +      if (!cmit)
        +              usage(describe_usage);
               if (!initialized) {
                       initialized = 1;

    1. It is preceded with a "git diff" header, that looks like this (when
       -c option is used):

           diff --combined file

       or like this (when --cc option is used):

           diff --cc file

    2. It is followed by one or more extended header lines (this example
       shows a merge with two parents):

           index <hash>,<hash>..<hash>
           mode <mode>,<mode>..<mode>
           new file mode <mode>
           deleted file mode <mode>,<mode>

       The mode <mode>,<mode>..<mode> line appears only if at least one of
       the <mode> is different from the rest. Extended headers with
       information about detected contents movement (renames and copying
       detection) are designed to work with diff of two <tree-ish> and are
       not used by combined diff format.

    3. It is followed by two-line from-file/to-file header

           --- a/file
           +++ b/file

       Similar to two-line header for traditional unified diff format,
       /dev/null is used to signal created or deleted files.

    4. Chunk header format is modified to prevent people from accidentally
       feeding it to patch -p1. Combined diff format was created for
       review of merge commit changes, and was not meant for apply. The
       change is similar to the change in the extended index header:

           @@@ <from-file-range> <from-file-range> <to-file-range> @@@

       There are (number of parents + 1) @ characters in the chunk header
       for combined diff format.

   Unlike the traditional unified diff format, which shows two files A and
   B with a single column that has - (minus --- appears in A but removed in
   B), + (plus --- missing in A but added to B), or " " (space --- unchanged)
   prefix, this format compares two or more files file1, file2,... with
   one file X, and shows how X differs from each of fileN. One column for
   each of fileN is prepended to the output line to note how X's line is
   different from it.

   A - character in the column N means that the line appears in fileN but
   it does not appear in the result. A + character in the column N means
   that the line appears in the result, and fileN does not have that line
   (in other words, the line was added, from the point of view of that

   In the above example output, the function signature was changed from
   both files (hence two - removals from both file1 and file2, plus ++ to
   mean one line that was added does not appear in either file1 or file2).
   Also eight other lines are the same from file1 but do not appear in
   file2 (hence prefixed with +).

   When shown by git diff-tree -c, it compares the parents of a merge
   commit with the merge result (i.e. file1..fileN are the parents). When
   shown by git diff-files -c, it compares the two unresolved merge
   parents with the working tree file (i.e. file1 is stage 2 aka "our
   version", file2 is stage 3 aka "their version").


   The --summary option describes newly added, deleted, renamed and copied
   files. The --stat option adds diffstat(1) graph to the output. These
   options can be combined with other options, such as -p, and are meant
   for human consumption.

   When showing a change that involves a rename or a copy, --stat output
   formats the pathnames compactly by combining common prefix and suffix
   of the pathnames. For example, a change that moves arch/i386/Makefile
   to arch/x86/Makefile while modifying 4 lines will be shown like this:

       arch/{i386 => x86}/Makefile    |   4 +--

   The --numstat option gives the diffstat(1) information but is designed
   for easier machine consumption. An entry in --numstat output looks like

       1       2       README
       3       1       arch/{i386 => x86}/Makefile

   That is, from left to right:

    1. the number of added lines;

    2. a tab;

    3. the number of deleted lines;

    4. a tab;

    5. pathname (possibly with rename/copy information);

    6. a newline.

   When -z output option is in effect, the output is formatted this way:

       1       2       README NUL
       3       1       NUL arch/i386/Makefile NUL arch/x86/Makefile NUL

   That is:

    1. the number of added lines;

    2. a tab;

    3. the number of deleted lines;

    4. a tab;

    5. a NUL (only exists if renamed/copied);

    6. pathname in preimage;

    7. a NUL (only exists if renamed/copied);

    8. pathname in postimage (only exists if renamed/copied);

    9. a NUL.

   The extra NUL before the preimage path in renamed case is to allow
   scripts that read the output to tell if the current record being read
   is a single-path record or a rename/copy record without reading ahead.
   After reading added and deleted lines, reading up to NUL would yield
   the pathname, but if that is NUL, the record will show two paths.


   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.


   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 using 'git write-tree')

   For example, let's say that you have worked on your working directory,
   updated some files in the index and are ready to commit. You want to
   see exactly what you are going to commit, without having to write a new
   tree object and compare it that way, and to do that, you just do

       git diff-index --cached HEAD

   Example: let's say I had renamed commit.c to git-commit.c, and I had
   done an update-index 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-index does:

       torvalds@ppc970:~/git> git diff-index --cached HEAD
       -100644 blob    4161aecc6700a2eb579e842af0b7f22b98443f74        commit.c
       +100644 blob    4161aecc6700a2eb579e842af0b7f22b98443f74        git-commit.c

   You can see easily that the above is a rename.

   In fact, git diff-index --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-index --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".


   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 index, 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-index on it yet - there is no "object"
   associated with the new state, and you get:

       torvalds@ppc970:~/v2.6/linux> git diff-index --abbrev HEAD
       :100644 100664 7476bb... 000000...      kernel/sched.c

   i.e., 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.

       As with other commands of this type, git diff-index 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
       update-index it to make the index be in sync.

       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.


   Part of the git(1) suite


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