git-diff-index(1)



GIT-DIFF-INDEX(1)                 Git Manual                 GIT-DIFF-INDEX(1)

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

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

DESCRIPTION
       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.

OPTIONS
       -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.

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

       --patch-with-raw
           Synonym for -p --raw.

       --indent-heuristic, --no-indent-heuristic
           These are to help debugging and tuning experimental heuristics
           (which are off by default) that shift diff hunk boundaries to make
           patches easier to read.

       --minimal
           Spend extra time to make sure the smallest possible diff is
           produced.

       --patience
           Generate a diff using the "patience diff" algorithm.

       --histogram
           Generate a diff using the "histogram diff" algorithm.

       --diff-algorithm={patience|minimal|histogram|myers}
           Choose a diff algorithm. The variants are as follows:

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

           minimal
               Spend extra time to make sure the smallest possible diff is
               produced.

           patience
               Use "patience diff" algorithm when generating patches.

           histogram
               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.

       --stat[=<width>[,<name-width>[,<count>]]]
           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
           --stat-count=<count>.

       --numstat
           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.

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

       --dirstat[=<param1,param2,...>]
           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:

           changes
               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.

           lines
               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.

           files
               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.

           cumulative
               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.

           <limit>
               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.

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

       --patch-with-stat
           Synonym for -p --stat.

       -z
           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, pathnames with "unusual" characters are quoted
           as explained for the configuration variable core.quotePath (see
           git-config(1)).

       --name-only
           Show only names of changed files.

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

       --submodule[=<format>]
           Specify how differences in submodules are shown. When specifying
           --submodule=short the short format is used. This format just shows
           the names of the commits at the beginning and end of the range.
           When --submodule or --submodule=log is specified, the log format is
           used. This format lists the commits in the range like git-
           submodule(1) summary does. When --submodule=diff is specified, the
           diff format is used. This format shows an inline diff of the
           changes in the submodule contents between the commit range.
           Defaults to diff.submodule or the short format if the config option
           is unset.

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

       --no-color
           Turn off colored diff. It is the same as --color=never.

       --word-diff[=<mode>]
           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:

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

           plain
               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.

           porcelain
               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.

           none
               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.

       --word-diff-regex=<regex>
           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.

       --color-words[=<regex>]
           Equivalent to --word-diff=color plus (if a regex was specified)
           --word-diff-regex=<regex>.

       --no-renames
           Turn off rename detection, even when the configuration file gives
           the default to do so.

       --check
           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.

       --ws-error-highlight=<kind>
           Highlight whitespace errors in the context, old or new lines of the
           diff. Multiple values are separated by comma, none resets previous
           values, default reset the list to new and all is a shorthand for
           old,new,context. When this option is not given, and the
           configuration variable diff.wsErrorHighlight is not set, only
           whitespace errors in new lines are highlighted. The whitespace
           errors are colored whith color.diff.whitespace.

       --full-index
           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.

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

       --abbrev[=<n>]
           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>.

       --find-copies-harder
           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 lacks 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.

       -l<num>
           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.

       --diff-filter=[(A|C|D|M|R|T|U|X|B)...[*]]
           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
           selected.

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

       -S<string>
           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.

       -G<regex>
           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
           file:

               +    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.

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

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

       -O<orderfile>
           Control the order in which files appear in the output. This
           overrides the diff.orderFile configuration variable (see git-
           config(1)). To cancel diff.orderFile, use -O/dev/null.

           The output order is determined by the order of glob patterns in
           <orderfile>. All files with pathnames that match the first pattern
           are output first, all files with pathnames that match the second
           pattern (but not the first) are output next, and so on. All files
           with pathnames that do not match any pattern are output last, as if
           there was an implicit match-all pattern at the end of the file. If
           multiple pathnames have the same rank (they match the same pattern
           but no earlier patterns), their output order relative to each other
           is the normal order.

           <orderfile> is parsed as follows:

           o   Blank lines are ignored, so they can be used as separators for
               readability.

           o   Lines starting with a hash ("#") are ignored, so they can be
               used for comments. Add a backslash ("\") to the beginning of
               the pattern if it starts with a hash.

           o   Each other line contains a single pattern.

           Patterns have the same syntax and semantics as patterns used for
           fnmantch(3) without the FNM_PATHNAME flag, except a pathname also
           matches a pattern if removing any number of the final pathname
           components matches the pattern. For example, the pattern "foo*bar"
           matches "fooasdfbar" and "foo/bar/baz/asdf" but not "foobarx".

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

       --relative[=<path>]
           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-space-at-eol
           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-blank-lines
           Ignore changes whose lines are all blank.

       --inter-hunk-context=<lines>
           Show the context between diff hunks, up to the specified number of
           lines, thereby fusing hunks that are close to each other. Defaults
           to diff.interHunkContext or 0 if the config option is unset.

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

       --exit-code
           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.

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

       --ext-diff
           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.

       --no-ext-diff
           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-submodules[=<when>]
           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.

       --src-prefix=<prefix>
           Show the given source prefix instead of "a/".

       --dst-prefix=<prefix>
           Show the given destination prefix instead of "b/".

       --no-prefix
           Do not show any source or destination prefix.

       --line-prefix=<prefix>
           Prepend an additional prefix to every line of output.

       --ita-invisible-in-index
           By default entries added by "git add -N" appear as an existing
           empty file in "git diff" and a new file in "git diff --cached".
           This option makes the entry appear as a new file in "git diff" and
           non-existent in "git diff --cached". This option could be reverted
           with --ita-visible-in-index. Both options are experimental and
           could be removed in future.

       For more detailed explanation on these common options, see also
       gitdiffcore(7).

       <tree-ish>
           The id of a tree object to diff against.

       --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-index say that all
           non-checked-out files are up to date.

RAW OUTPUT FORMAT
       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
       differs:

       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:

       o   A: addition of a file

       o   C: copy of a file into a new one

       o   D: deletion of a file

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

       o   R: renaming of a file

       o   T: change in the type of the file

       o   U: file is unmerged (you must complete the merge before it can be
           committed)

       o   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.

       Example:

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

       Without the -z option, pathnames with "unusual" characters are quoted
       as explained for the configuration variable core.quotePath (see git-
       config(1)). Using -z the filename is output verbatim and the line is
       terminated by a NUL byte.

DIFF FORMAT FOR MERGES
       "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"

       Example:

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

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

GENERATING PATCHES WITH -P
       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/
           prefixes.

           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. Pathnames with "unusual" characters are quoted as explained for the
           configuration variable core.quotePath (see git-config(1)).

        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

COMBINED DIFF FORMAT
       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;
                           for_each_ref(get_name);

        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
       parent).

       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").

OTHER DIFF FORMATS
       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
       this:

           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.

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 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".

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 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.

           Note
           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.

           Note
           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.

GIT
       Part of the git(1) suite

Git 2.14.2                        09/26/2017                 GIT-DIFF-INDEX(1)

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