difftool: Add '-x' and as an alias for '--extcmd'

This adds '-x' as a shorthand for the '--extcmd' option.
Arguments to '--extcmd' can be specified separately, which
was not originally possible.

This also fixes the brief help text so that it mentions
both '-x' and '--extcmd'.

Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-difftool.txt

@@ -7,7 +7,7 @@ git-difftool - Show changes using common diff tools
 
 SYNOPSIS
 --------
-'git difftool' [--tool=<tool>] [-y|--no-prompt|--prompt] [<'git diff' options>]
+'git difftool' [<options>] <commit>{0,2} [--] [<path>...]
 
 DESCRIPTION
 -----------
@@ -58,6 +58,7 @@ is set to the name of the temporary file containing the contents
 of the diff post-image.  `$BASE` is provided for compatibility
 with custom merge tool commands and has the same value as `$LOCAL`.
 
+-x <command>::
 --extcmd=<command>::
 	Specify a custom command for viewing diffs.
 	'git-difftool' ignores the configured defaults and runs

git-difftool.perl

@@ -1,5 +1,5 @@
 #!/usr/bin/env perl
-# Copyright (c) 2009 David Aguilar
+# Copyright (c) 2009, 2010 David Aguilar
 #
 # This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
 # git-difftool--helper script.
@@ -23,8 +23,9 @@ my $DIR = abs_path(dirname($0));
 sub usage
 {
 	print << 'USAGE';
-usage: git difftool [-g|--gui] [-t|--tool=<tool>] [-y|--no-prompt]
-                    ["git diff" options]
+usage: git difftool [-t|--tool=<tool>] [-x|--extcmd=<cmd>]
+                    [-y|--no-prompt]   [-g|--gui]
+                    ['git diff' options]
 USAGE
 	exit 1;
 }
@@ -62,14 +63,20 @@ sub generate_command
 			$skip_next = 1;
 			next;
 		}
-		if ($arg =~ /^--extcmd=/) {
-			$ENV{GIT_DIFFTOOL_EXTCMD} = substr($arg, 9);
-			next;
-		}
 		if ($arg =~ /^--tool=/) {
 			$ENV{GIT_DIFF_TOOL} = substr($arg, 7);
 			next;
 		}
+		if ($arg eq '-x' || $arg eq '--extcmd') {
+			usage() if $#ARGV <= $idx;
+			$ENV{GIT_DIFFTOOL_EXTCMD} = $ARGV[$idx + 1];
+			$skip_next = 1;
+			next;
+		}
+		if ($arg =~ /^--extcmd=/) {
+			$ENV{GIT_DIFFTOOL_EXTCMD} = substr($arg, 9);
+			next;
+		}
 		if ($arg eq '-g' || $arg eq '--gui') {
 			my $tool = Git::command_oneline('config',
 			                                'diff.guitool');

t/t7800-difftool.sh

@@ -225,8 +225,16 @@ test_expect_success 'difftool.<tool>.path' '
 test_expect_success 'difftool --extcmd=cat' '
 	diff=$(git difftool --no-prompt --extcmd=cat branch) &&
 	test "$diff" = branch"$LF"master
+'
 
+test_expect_success 'difftool --extcmd cat' '
+	diff=$(git difftool --no-prompt --extcmd cat branch) &&
+	test "$diff" = branch"$LF"master
+'
 
+test_expect_success 'difftool -x cat' '
+	diff=$(git difftool --no-prompt -x cat branch) &&
+	test "$diff" = branch"$LF"master
 
 
 '