Documentation/diff-generate-patch.txt

   1 Generating patch text with -p
   2 -----------------------------
   3
   4 Running
   5 linkgit:git-diff[1],
   6 linkgit:git-log[1],
   7 linkgit:git-show[1],
   8 linkgit:git-diff-index[1],
   9 linkgit:git-diff-tree[1], or
  10 linkgit:git-diff-files[1]
  11 with the `-p` option produces patch text.
  12 You can customize the creation of patch text via the
  13 `GIT_EXTERNAL_DIFF` and the `GIT_DIFF_OPTS` environment variables
  14 (see linkgit:git[1]).
  15
  16 What the -p option produces is slightly different from the traditional
  17 diff format:
  18
  19 1.   It is preceded with a "git diff" header that looks like this:
  20
  21        diff --git a/file1 b/file2
  22 +
  23 The `a/` and `b/` filenames are the same unless rename/copy is
  24 involved.  Especially, even for a creation or a deletion,
  25 `/dev/null` is _not_ used in place of the `a/` or `b/` filenames.
  26 +
  27 When rename/copy is involved, `file1` and `file2` show the
  28 name of the source file of the rename/copy and the name of
  29 the file that rename/copy produces, respectively.
  30
  31 2.   It is followed by one or more extended header lines:
  32
  33        old mode <mode>
  34        new mode <mode>
  35        deleted file mode <mode>
  36        new file mode <mode>
  37        copy from <path>
  38        copy to <path>
  39        rename from <path>
  40        rename to <path>
  41        similarity index <number>
  42        dissimilarity index <number>
  43        index <hash>..<hash> <mode>
  44 +
  45 File modes are printed as 6-digit octal numbers including the file type
  46 and file permission bits.
  47 +
  48 Path names in extended headers do not include the `a/` and `b/` prefixes.
  49 +
  50 The similarity index is the percentage of unchanged lines, and
  51 the dissimilarity index is the percentage of changed lines.  It
  52 is a rounded down integer, followed by a percent sign.  The
  53 similarity index value of 100% is thus reserved for two equal
  54 files, while 100% dissimilarity means that no line from the old
  55 file made it into the new one.
  56 +
  57 The index line includes the blob object names before and after the change.
  58 The <mode> is included if the file mode does not change; otherwise,
  59 separate lines indicate the old and the new mode.
  60
  61 3.  Pathnames with "unusual" characters are quoted as explained for
  62     the configuration variable `core.quotePath` (see
  63     linkgit:git-config[1]).
  64
  65 4.  All the `file1` files in the output refer to files before the
  66     commit, and all the `file2` files refer to files after the commit.
  67     It is incorrect to apply each change to each file sequentially.  For
  68     example, this patch will swap a and b:
  69
  70       diff --git a/a b/b
  71       rename from a
  72       rename to b
  73       diff --git a/b b/a
  74       rename from b
  75       rename to a
  76
  77
  78 Combined diff format
  79 --------------------
  80
  81 Any diff-generating command can take the `-c` or `--cc` option to
  82 produce a 'combined diff' when showing a merge. This is the default
  83 format when showing merges with linkgit:git-diff[1] or
  84 linkgit:git-show[1]. Note also that you can give the `-m` option to any
  85 of these commands to force generation of diffs with individual parents
  86 of a merge.
  87
  88 A "combined diff" format looks like this:
  89
  90 ------------
  91 diff --combined describe.c
  92 index fabadb8,cc95eb0..4866510
  93 --- a/describe.c
  94 +++ b/describe.c
  95 @@@ -98,20 -98,12 +98,20 @@@
  96         return (a_date > b_date) ? -1 : (a_date == b_date) ? 0 : 1;
  97   }
  98
  99 - static void describe(char *arg)
 100  -static void describe(struct commit *cmit, int last_one)
 101 ++static void describe(char *arg, int last_one)
 102   {
 103  +      unsigned char sha1[20];
 104  +      struct commit *cmit;
 105         struct commit_list *list;
 106         static int initialized = 0;
 107         struct commit_name *n;
 108
 109  +      if (get_sha1(arg, sha1) < 0)
 110  +              usage(describe_usage);
 111  +      cmit = lookup_commit_reference(sha1);
 112  +      if (!cmit)
 113  +              usage(describe_usage);
 114  +
 115         if (!initialized) {
 116                 initialized = 1;
 117                 for_each_ref(get_name);
 118 ------------
 119
 120 1.   It is preceded with a "git diff" header, that looks like
 121      this (when the `-c` option is used):
 122
 123        diff --combined file
 124 +
 125 or like this (when the `--cc` option is used):
 126
 127        diff --cc file
 128
 129 2.   It is followed by one or more extended header lines
 130      (this example shows a merge with two parents):
 131
 132        index <hash>,<hash>..<hash>
 133        mode <mode>,<mode>..<mode>
 134        new file mode <mode>
 135        deleted file mode <mode>,<mode>
 136 +
 137 The `mode <mode>,<mode>..<mode>` line appears only if at least one of
 138 the <mode> is different from the rest. Extended headers with
 139 information about detected contents movement (renames and
 140 copying detection) are designed to work with diff of two
 141 <tree-ish> and are not used by combined diff format.
 142
 143 3.   It is followed by two-line from-file/to-file header
 144
 145        --- a/file
 146        +++ b/file
 147 +
 148 Similar to two-line header for traditional 'unified' diff
 149 format, `/dev/null` is used to signal created or deleted
 150 files.
 151 +
 152 However, if the --combined-all-paths option is provided, instead of a
 153 two-line from-file/to-file you get a N+1 line from-file/to-file header,
 154 where N is the number of parents in the merge commit
 155
 156        --- a/file
 157        --- a/file
 158        --- a/file
 159        +++ b/file
 160 +
 161 This extended format can be useful if rename or copy detection is
 162 active, to allow you to see the original name of the file in different
 163 parents.
 164
 165 4.   Chunk header format is modified to prevent people from
 166      accidentally feeding it to `patch -p1`. Combined diff format
 167      was created for review of merge commit changes, and was not
 168      meant to be applied. The change is similar to the change in the
 169      extended 'index' header:
 170
 171        @@@ <from-file-range> <from-file-range> <to-file-range> @@@
 172 +
 173 There are (number of parents + 1) `@` characters in the chunk
 174 header for combined diff format.
 175
 176 Unlike the traditional 'unified' diff format, which shows two
 177 files A and B with a single column that has `-` (minus --
 178 appears in A but removed in B), `+` (plus -- missing in A but
 179 added to B), or `" "` (space -- unchanged) prefix, this format
 180 compares two or more files file1, file2,... with one file X, and
 181 shows how X differs from each of fileN.  One column for each of
 182 fileN is prepended to the output line to note how X's line is
 183 different from it.
 184
 185 A `-` character in the column N means that the line appears in
 186 fileN but it does not appear in the result.  A `+` character
 187 in the column N means that the line appears in the result,
 188 and fileN does not have that line (in other words, the line was
 189 added, from the point of view of that parent).
 190
 191 In the above example output, the function signature was changed
 192 from both files (hence two `-` removals from both file1 and
 193 file2, plus `++` to mean one line that was added does not appear
 194 in either file1 or file2).  Also eight other lines are the same
 195 from file1 but do not appear in file2 (hence prefixed with `+`).
 196
 197 When shown by `git diff-tree -c`, it compares the parents of a
 198 merge commit with the merge result (i.e. file1..fileN are the
 199 parents).  When shown by `git diff-files -c`, it compares the
 200 two unresolved merge parents with the working tree file
 201 (i.e. file1 is stage 2 aka "our version", file2 is stage 3 aka
 202 "their version").