[PATCH 2/2] difftool: don't assume that default sh is sane

[Charles Bailey <charles@hashpling.org>]

From: Charles Bailey <cbailey32@bloomberg.net>

git-difftool used to create a command list script containing $( ... )
and explicitly call "sh -c" with this list.

Instead, allow mergetool --tool-help to take a mode parameter and call
mergetool directly to invoke the show_tool_help function. This mode
parameter is intented for use solely by difftool.

Signed-off-by: Charles Bailey <cbailey32@bloomberg.net>
---
Another issue for Solaris. Originally I had a fix for this that
substituted "@SHELL_PATH@" even inside perl scripts but I felt that
having an interface for show_tool_help was a little neater all round but
I welcome alternative views.

 git-difftool.perl |  6 +-----
 git-mergetool.sh  | 12 +++++++++++-
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/git-difftool.perl b/git-difftool.perl
index 18ca61e..598fcc2 100755
--- a/git-difftool.perl
+++ b/git-difftool.perl
@@ -47,13 +47,9 @@ sub find_worktree
 
 sub print_tool_help
 {
-	my $cmd = 'TOOL_MODE=diff';
-	$cmd .= ' && . "$(git --exec-path)/git-mergetool--lib"';
-	$cmd .= ' && show_tool_help';
-
 	# See the comment at the bottom of file_diff() for the reason behind
 	# using system() followed by exit() instead of exec().
-	my $rc = system('sh', '-c', $cmd);
+	my $rc = system(qw(git mergetool --tool-help=diff));
 	exit($rc | ($rc >> 8));
 }
 
diff --git a/git-mergetool.sh b/git-mergetool.sh
index e969dd0..d32b663 100755
--- a/git-mergetool.sh
+++ b/git-mergetool.sh
@@ -320,7 +320,17 @@ guessed_merge_tool=false
 while test $# != 0
 do
 	case "$1" in
-	--tool-help)
+	--tool-help*)
+		case "$#,$1" in
+		1,*=*)
+			TOOL_MODE=$(expr "z$1" : 'z-[^=]*=\(.*\)')
+			;;
+		1,--tool-help)
+			;;
+		*)
+			usage
+			;;
+		esac
 		show_tool_help
 		;;
 	-t|--tool*)
-- 
2.0.2.611.g8c85416