[PATCH/RFC] grep: optionally show only the match

Make git-grep optionally omit the parts of the line before and after the
match.

Signed-off-by: Marcus Karlsson <redacted>
---
  Documentation/git-grep.txt | 8 +++++++-
  builtin/grep.c             | 2 ++
  grep.c                     | 7 +++++--
  grep.h                     | 1 +
  4 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt
index cfecf84..6ef22cb 100644
--- a/Documentation/git-grep.txt
+++ b/Documentation/git-grep.txt

@@ -20,7 +20,8 @@ SYNOPSIS
  	   [-c | --count] [--all-match] [-q | --quiet]
  	   [--max-depth <depth>]
  	   [--color[=<when>] | --no-color]
-	   [--break] [--heading] [-p | --show-function]
+	   [--break] [--heading] [-o | --only-matching]
+	   [-p | --show-function]
  	   [-A <post-context>] [-B <pre-context>] [-C <context>]
  	   [-W | --function-context]
  	   [-f <file>] [-e] <pattern>

@@ -183,6 +184,11 @@ OPTIONS
  	Show the filename above the matches in that file instead of
  	at the start of each shown line.

+-o::
+--only-matching::
+	Show only the part of the matching line that matched the
+	pattern.
+
  -p::
  --show-function::
  	Show the preceding line that contains the function name of

diff --git a/builtin/grep.c b/builtin/grep.c
index 09ca4c9..56aba7b 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c

@@ -782,6 +782,8 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
  			N_("print empty line between matches from different files")),
  		OPT_BOOLEAN(0, "heading", &opt.heading,
  			N_("show filename only once above matches from same file")),
+		OPT_BOOLEAN('o', "only-matching", &opt.only_matching,
+			N_("show only the matching part of a matched line")),
  		OPT_GROUP(""),
  		OPT_CALLBACK('C', "context", &opt, N_("n"),
  			N_("show <n> context lines before and after matches"),

diff --git a/grep.c b/grep.c
index 04e3ec6..9fc888e 100644
--- a/grep.c
+++ b/grep.c

@@ -827,7 +827,9 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
  			if (match.rm_so == match.rm_eo)
  				break;

-			output_color(opt, bol, match.rm_so, line_color);
+			if (opt->only_matching == 0)
+				output_color(opt, bol, match.rm_so,
+					     line_color);
  			output_color(opt, bol + match.rm_so,
  				     match.rm_eo - match.rm_so,
  				     opt->color_match);

@@ -837,7 +839,8 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
  		}
  		*eol = ch;
  	}
-	output_color(opt, bol, rest, line_color);
+	if (opt->only_matching == 0)
+		output_color(opt, bol, rest, line_color);
  	opt->output(opt, "\n", 1);
  }