contrib/git-jump: allow to configure the grep command

Add the configuration option "jump.grepCmd" that allows to configure the
command that is used to search in grep mode. This allows the users of
git-jump to use ag(1) or ack(1) as search engines.

Signed-off-by: Beat Bolli <dev+git@drbeat.li>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/git-jump/README

@@ -63,6 +63,9 @@ git jump grep foo_bar
 # same as above, but case-insensitive; you can give
 # arbitrary grep options
 git jump grep -i foo_bar
+
+# use the silver searcher for git jump grep
+git config jump.grepCmd "ag --column"
 --------------------------------------------------
 
 

contrib/git-jump/git-jump

@@ -11,7 +11,8 @@ diff: elements are diff hunks. Arguments are given to diff.
 
 merge: elements are merge conflicts. Arguments are ignored.
 
-grep: elements are grep hits. Arguments are given to grep.
+grep: elements are grep hits. Arguments are given to git grep or, if
+      configured, to the command in `jump.grepCmd`.
 
 ws: elements are whitespace errors. Arguments are given to diff --check.
 EOF
@@ -50,7 +51,9 @@ mode_merge() {
 # but let's clean up extra whitespace, so they look better if the
 # editor shows them to us in the status bar.
 mode_grep() {
-	git grep -n "$@" |
+	cmd=$(git config jump.grepCmd)
+	test -n "$cmd" || cmd="git grep -n"
+	$cmd "$@" |
 	perl -pe '
 	s/[ \t]+/ /g;
 	s/^ *//;