contrib: add 'git difftool' for launching common merge tools

'git difftool' is a git command that allows you to compare and edit files
between revisions using common merge tools.  'git difftool' does what
'git mergetool' does but its use is for non-merge situations such as
when preparing commits or comparing changes against the index.
It uses the same configuration variables as 'git mergetool' and
provides the same command-line interface as 'git diff'.

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

1 files changed, 74 insertions, 0 deletions

diff --git a/contrib/difftool/git-difftool b/contrib/difftool/git-difftool
new file mode 100755
index 000000000..1fc087c5f
--- /dev/null
+++ b/contrib/difftool/git-difftool
@@ -0,0 +1,74 @@
+#!/usr/bin/env perl
+# Copyright (c) 2009 David Aguilar
+#
+# This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
+# git-difftool-helper script.  This script exports
+# GIT_EXTERNAL_DIFF and GIT_PAGER for use by git, and
+# GIT_NO_PROMPT and GIT_MERGE_TOOL for use by git-difftool-helper.
+# Any arguments that are unknown to this script are forwarded to 'git diff'.
+
+use strict;
+use warnings;
+use Cwd qw(abs_path);
+use File::Basename qw(dirname);
+
+my $DIR = abs_path(dirname($0));
+
+
+sub usage
+{
+	print << 'USAGE';
+
+usage: git difftool [--no-prompt] [--tool=tool] ["git diff" options]
+USAGE
+	exit 1;
+}
+
+sub setup_environment
+{
+	$ENV{PATH} = "$DIR:$ENV{PATH}";
+	$ENV{GIT_PAGER} = '';
+	$ENV{GIT_EXTERNAL_DIFF} = 'git-difftool-helper';
+}
+
+sub exe
+{
+	my $exe = shift;
+	return defined $ENV{COMSPEC} ? "$exe.exe" : $exe;
+}
+
+sub generate_command
+{
+	my @command = (exe('git'), 'diff');
+	my $skip_next = 0;
+	my $idx = -1;
+	for my $arg (@ARGV) {
+		$idx++;
+		if ($skip_next) {
+			$skip_next = 0;
+			next;
+		}
+		if ($arg eq '-t' or $arg eq '--tool') {
+			usage() if $#ARGV <= $idx;
+			$ENV{GIT_MERGE_TOOL} = $ARGV[$idx + 1];
+			$skip_next = 1;
+			next;
+		}
+		if ($arg =~ /^--tool=/) {
+			$ENV{GIT_MERGE_TOOL} = substr($arg, 7);
+			next;
+		}
+		if ($arg eq '--no-prompt') {
+			$ENV{GIT_DIFFTOOL_NO_PROMPT} = 'true';
+			next;
+		}
+		if ($arg eq '-h' or $arg eq '--help') {
+			usage();
+		}
+		push @command, $arg;
+	}
+	return @command
+}
+
+setup_environment();
+exec(generate_command());