Documentation/diff-generate-patch.txt

   1 Generating patches with -p
   2 --------------------------
   3
   4 When "git-diff-index", "git-diff-tree", or "git-diff-files" are run
   5 with a '-p' option, "git diff" without the '--raw' option, or
   6 "git log" with the "-p" option, they
   7 do not produce the output described above; instead they produce a
   8 patch file.  You can customize the creation of such patches via the
   9 GIT_EXTERNAL_DIFF and the GIT_DIFF_OPTS environment variables.
  10
  11 What the -p option produces is slightly different from the traditional
  12 diff format:
  13
  14 1.   It is preceded with a "git diff" header that looks like this:
  15
  16        diff --git a/file1 b/file2
  17 +
  18 The `a/` and `b/` filenames are the same unless rename/copy is
  19 involved.  Especially, even for a creation or a deletion,
  20 `/dev/null` is _not_ used in place of the `a/` or `b/` filenames.
  21 +
  22 When rename/copy is involved, `file1` and `file2` show the
  23 name of the source file of the rename/copy and the name of
  24 the file that rename/copy produces, respectively.
  25
  26 2.   It is followed by one or more extended header lines:
  27
  28        old mode <mode>
  29        new mode <mode>
  30        deleted file mode <mode>
  31        new file mode <mode>
  32        copy from <path>
  33        copy to <path>
  34        rename from <path>
  35        rename to <path>
  36        similarity index <number>
  37        dissimilarity index <number>
  38        index <hash>..<hash> <mode>
  39 +
  40 File modes are printed as 6-digit octal numbers including the file type
  41 and file permission bits.
  42 +
  43 Path names in extended headers do not include the `a/` and `b/` prefixes.
  44 +
  45 The similarity index is the percentage of unchanged lines, and
  46 the dissimilarity index is the percentage of changed lines.  It
  47 is a rounded down integer, followed by a percent sign.  The
  48 similarity index value of 100% is thus reserved for two equal
  49 files, while 100% dissimilarity means that no line from the old
  50 file made it into the new one.
  51 +
  52 The index line includes the SHA-1 checksum before and after the change.
  53 The <mode> is included if the file mode does not change; otherwise,
  54 separate lines indicate the old and the new mode.
  55
  56 3.  TAB, LF, double quote and backslash characters in pathnames
  57     are represented as `\t`, `\n`, `\"` and `\\`, respectively.
  58     If there is need for such substitution then the whole
  59     pathname is put in double quotes.
  60
  61 4.  All the `file1` files in the output refer to files before the
  62     commit, and all the `file2` files refer to files after the commit.
  63     It is incorrect to apply each change to each file sequentially.  For
  64     example, this patch will swap a and b:
  65
  66       diff --git a/a b/b
  67       rename from a
  68       rename to b
  69       diff --git a/b b/a
  70       rename from b
  71       rename to a
  72
  73
  74 combined diff format
  75 --------------------
  76
  77 "git-diff-tree", "git-diff-files" and "git-diff" can take '-c' or
  78 '--cc' option to produce 'combined diff'.  For showing a merge commit
  79 with "git log -p", this is the default format; you can force showing
  80 full diff with the '-m' option.
  81 A 'combined diff' format looks like this:
  82
  83 ------------
  84 diff --combined describe.c
  85 index fabadb8,cc95eb0..4866510
  86 --- a/describe.c
  87 +++ b/describe.c
  88 @@@ -98,20 -98,12 +98,20 @@@
  89         return (a_date > b_date) ? -1 : (a_date == b_date) ? 0 : 1;
  90   }
  91
  92 - static void describe(char *arg)
  93  -static void describe(struct commit *cmit, int last_one)
  94 ++static void describe(char *arg, int last_one)
  95   {
  96  +      unsigned char sha1[20];
  97  +      struct commit *cmit;
  98         struct commit_list *list;
  99         static int initialized = 0;
 100         struct commit_name *n;
 101
 102  +      if (get_sha1(arg, sha1) < 0)
 103  +              usage(describe_usage);
 104  +      cmit = lookup_commit_reference(sha1);
 105  +      if (!cmit)
 106  +              usage(describe_usage);
 107  +
 108         if (!initialized) {
 109                 initialized = 1;
 110                 for_each_ref(get_name);
 111 ------------
 112
 113 1.   It is preceded with a "git diff" header, that looks like
 114      this (when '-c' option is used):
 115
 116        diff --combined file
 117 +
 118 or like this (when '--cc' option is used):
 119
 120        diff --cc file
 121
 122 2.   It is followed by one or more extended header lines
 123      (this example shows a merge with two parents):
 124
 125        index <hash>,<hash>..<hash>
 126        mode <mode>,<mode>..<mode>
 127        new file mode <mode>
 128        deleted file mode <mode>,<mode>
 129 +
 130 The `mode <mode>,<mode>..<mode>` line appears only if at least one of
 131 the <mode> is different from the rest. Extended headers with
 132 information about detected contents movement (renames and
 133 copying detection) are designed to work with diff of two
 134 <tree-ish> and are not used by combined diff format.
 135
 136 3.   It is followed by two-line from-file/to-file header
 137
 138        --- a/file
 139        +++ b/file
 140 +
 141 Similar to two-line header for traditional 'unified' diff
 142 format, `/dev/null` is used to signal created or deleted
 143 files.
 144
 145 4.   Chunk header format is modified to prevent people from
 146      accidentally feeding it to `patch -p1`. Combined diff format
 147      was created for review of merge commit changes, and was not
 148      meant for apply. The change is similar to the change in the
 149      extended 'index' header:
 150
 151        @@@ <from-file-range> <from-file-range> <to-file-range> @@@
 152 +
 153 There are (number of parents + 1) `@` characters in the chunk
 154 header for combined diff format.
 155
 156 Unlike the traditional 'unified' diff format, which shows two
 157 files A and B with a single column that has `-` (minus --
 158 appears in A but removed in B), `+` (plus -- missing in A but
 159 added to B), or `" "` (space -- unchanged) prefix, this format
 160 compares two or more files file1, file2,... with one file X, and
 161 shows how X differs from each of fileN.  One column for each of
 162 fileN is prepended to the output line to note how X's line is
 163 different from it.
 164
 165 A `-` character in the column N means that the line appears in
 166 fileN but it does not appear in the result.  A `+` character
 167 in the column N means that the line appears in the result,
 168 and fileN does not have that line (in other words, the line was
 169 added, from the point of view of that parent).
 170
 171 In the above example output, the function signature was changed
 172 from both files (hence two `-` removals from both file1 and
 173 file2, plus `++` to mean one line that was added does not appear
 174 in either file1 nor file2).  Also eight other lines are the same
 175 from file1 but do not appear in file2 (hence prefixed with `{plus}`).
 176
 177 When shown by `git diff-tree -c`, it compares the parents of a
 178 merge commit with the merge result (i.e. file1..fileN are the
 179 parents).  When shown by `git diff-files -c`, it compares the
 180 two unresolved merge parents with the working tree file
 181 (i.e. file1 is stage 2 aka "our version", file2 is stage 3 aka
 182 "their version").