docs/git-blame: explain more clearly the example pickaxe use

[thirdparty/git.git] / Documentation / git-blame.txt

git-blame(1)
============

NAME
----
git-blame - Show what revision and author last modified each line of a file

SYNOPSIS
--------
[verse]
'git blame' [-c] [-b] [-l] [--root] [-t] [-f] [-n] [-s] [-e] [-p] [-w] [--incremental]
	    [-L <range>] [-S <revs-file>] [-M] [-C] [-C] [-C] [--since=<date>]
	    [--abbrev=<n>] [<rev> | --contents <file> | --reverse <rev>] [--] <file>

DESCRIPTION
-----------

Annotates each line in the given file with information from the revision which
last modified the line. Optionally, start annotating from the given revision.

When specified one or more times, `-L` restricts annotation to the requested
lines.

The origin of lines is automatically followed across whole-file
renames (currently there is no option to turn the rename-following
off). To follow lines moved from one file to another, or to follow
lines that were copied and pasted from another file, etc., see the
`-C` and `-M` options.

The report does not tell you anything about lines which have been deleted or
replaced; you need to use a tool such as 'git diff' or the "pickaxe"
interface briefly mentioned in the following paragraph.

Apart from supporting file annotation, Git also supports searching the
development history for when a code snippet occurred in a change. This makes it
possible to track when a code snippet was added to a file, moved or copied
between files, and eventually deleted or replaced. It works by searching for
a text string in the diff. A small example of the pickaxe interface
that searches for `blame_usage`:

-----------------------------------------------------------------------------
$ git log --pretty=oneline -S'blame_usage'
5040f17eba15504bad66b14a645bddd9b015ebb7 blame -S <ancestry-file>
ea4c7f9bf69e781dd0cd88d2bccb2bf5cc15c9a7 git-blame: Make the output
-----------------------------------------------------------------------------

OPTIONS
-------
include::blame-options.txt[]

-c::
	Use the same output mode as linkgit:git-annotate[1] (Default: off).

--score-debug::
	Include debugging information related to the movement of
	lines between files (see `-C`) and lines moved within a
	file (see `-M`).  The first number listed is the score.
	This is the number of alphanumeric characters detected
	as having been moved between or within files.  This must be above
	a certain threshold for 'git blame' to consider those lines
	of code to have been moved.

-f::
--show-name::
	Show the filename in the original commit.  By default
	the filename is shown if there is any line that came from a
	file with a different name, due to rename detection.

-n::
--show-number::
	Show the line number in the original commit (Default: off).

-s::
	Suppress the author name and timestamp from the output.

-e::
--show-email::
	Show the author email instead of author name (Default: off).

-w::
	Ignore whitespace when comparing the parent's version and
	the child's to find where the lines came from.

--abbrev=<n>::
	Instead of using the default 7+1 hexadecimal digits as the
	abbreviated object name, use <n>+1 digits. Note that 1 column
	is used for a caret to mark the boundary commit.


THE PORCELAIN FORMAT
--------------------

In this format, each line is output after a header; the
header at the minimum has the first line which has:

- 40-byte SHA-1 of the commit the line is attributed to;
- the line number of the line in the original file;
- the line number of the line in the final file;
- on a line that starts a group of lines from a different
  commit than the previous one, the number of lines in this
  group.  On subsequent lines this field is absent.

This header line is followed by the following information
at least once for each commit:

- the author name ("author"), email ("author-mail"), time
  ("author-time"), and time zone ("author-tz"); similarly
  for committer.
- the filename in the commit that the line is attributed to.
- the first line of the commit log message ("summary").

The contents of the actual line is output after the above
header, prefixed by a TAB. This is to allow adding more
header elements later.

The porcelain format generally suppresses commit information that has
already been seen. For example, two lines that are blamed to the same
commit will both be shown, but the details for that commit will be shown
only once. This is more efficient, but may require more state be kept by
the reader. The `--line-porcelain` option can be used to output full
commit information for each line, allowing simpler (but less efficient)
usage like:

	# count the number of lines attributed to each author
	git blame --line-porcelain file |
	sed -n 's/^author //p' |
	sort | uniq -c | sort -rn


SPECIFYING RANGES
-----------------

Unlike 'git blame' and 'git annotate' in older versions of git, the extent
of the annotation can be limited to both line ranges and revision
ranges. The `-L` option, which limits annotation to a range of lines, may be
specified multiple times.

When you are interested in finding the origin for
lines 40-60 for file `foo`, you can use the `-L` option like so
(they mean the same thing -- both ask for 21 lines starting at
line 40):

	git blame -L 40,60 foo
	git blame -L 40,+21 foo

Also you can use a regular expression to specify the line range:

	git blame -L '/^sub hello {/,/^}$/' foo

which limits the annotation to the body of the `hello` subroutine.

When you are not interested in changes older than version
v2.6.18, or changes older than 3 weeks, you can use revision
range specifiers  similar to 'git rev-list':

	git blame v2.6.18.. -- foo
	git blame --since=3.weeks -- foo

When revision range specifiers are used to limit the annotation,
lines that have not changed since the range boundary (either the
commit v2.6.18 or the most recent commit that is more than 3
weeks old in the above example) are blamed for that range
boundary commit.

A particularly useful way is to see if an added file has lines
created by copy-and-paste from existing files.  Sometimes this
indicates that the developer was being sloppy and did not
refactor the code properly.  You can first find the commit that
introduced the file with:

	git log --diff-filter=A --pretty=short -- foo

and then annotate the change between the commit and its
parents, using `commit^!` notation:

	git blame -C -C -f $commit^! -- foo


INCREMENTAL OUTPUT
------------------

When called with `--incremental` option, the command outputs the
result as it is built.  The output generally will talk about
lines touched by more recent commits first (i.e. the lines will
be annotated out of order) and is meant to be used by
interactive viewers.

The output format is similar to the Porcelain format, but it
does not contain the actual lines from the file that is being
annotated.

. Each blame entry always starts with a line of:

	<40-byte hex sha1> <sourceline> <resultline> <num_lines>
+
Line numbers count from 1.

. The first time that a commit shows up in the stream, it has various
  other information about it printed out with a one-word tag at the
  beginning of each line describing the extra commit information (author,
  email, committer, dates, summary, etc.).

. Unlike the Porcelain format, the filename information is always
  given and terminates the entry:

	"filename" <whitespace-quoted-filename-goes-here>
+
and thus it is really quite easy to parse for some line- and word-oriented
parser (which should be quite natural for most scripting languages).
+
[NOTE]
For people who do parsing: to make it more robust, just ignore any
lines between the first and last one ("<sha1>" and "filename" lines)
where you do not recognize the tag words (or care about that particular
one) at the beginning of the "extended information" lines. That way, if
there is ever added information (like the commit encoding or extended
commit commentary), a blame viewer will not care.


MAPPING AUTHORS
---------------

include::mailmap.txt[]


SEE ALSO
--------
linkgit:git-annotate[1]

GIT
---
Part of the linkgit:git[1] suite