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diff --git a/Documentation/diff-generate-patch.txt b/Documentation/diff-generate-patch.txt new file mode 100644 index 0000000..c78063d --- /dev/null +++ b/Documentation/diff-generate-patch.txt @@ -0,0 +1,207 @@ +Generating patch text with -p +----------------------------- + +Running +linkgit:git-diff[1], +linkgit:git-log[1], +linkgit:git-show[1], +linkgit:git-diff-index[1], +linkgit:git-diff-tree[1], or +linkgit:git-diff-files[1] +with the `-p` option produces patch text. +You can customize the creation of patch text via the +`GIT_EXTERNAL_DIFF` and the `GIT_DIFF_OPTS` environment variables +(see linkgit:git[1]), and the `diff` attribute (see linkgit:gitattributes[5]). + +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 blob object names 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 + linkgit: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 + +5. Hunk headers mention the name of the function to which the hunk + applies. See "Defining a custom hunk-header" in + linkgit:gitattributes[5] for details of how to tailor to this to + specific languages. + + +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 linkgit:git-diff[1] or +linkgit:git-show[1]. Note also that you can give suitable +`--diff-merges` option to any of these commands to force generation of +diffs in specific format. + +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 the `-c` option is used): + + diff --combined file ++ +or like this (when the `--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. ++ +However, if the --combined-all-paths option is provided, instead of a +two-line from-file/to-file you get a N+1 line from-file/to-file header, +where N is the number of parents in the merge commit + + --- a/file + --- a/file + --- a/file + +++ b/file ++ +This extended format can be useful if rename or copy detection is +active, to allow you to see the original name of the file in different +parents. + +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 to be applied. 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"). |