difftool: don't assume that default sh is sane

diff --git a/git-difftool.perl b/git-difftool.perl
index 18ca61e8d0493bde9c21ed337043bc72fa5c73a7..598fcc23b930832a8cd3cfcff0c0d0c84ecd32bc 100755 (executable)
--- 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));
 }