annotate: display usage information if no filename was given

Signed-off-by: Matthias Kestenholz <matthias@spinlock.ch>

git-annotate.perl

@@ -10,9 +10,10 @@
 use strict;
 use Getopt::Long;
 use POSIX qw(strftime gmtime);
+use File::Basename qw(basename dirname);
 
 sub usage() {
-	print STDERR 'Usage: ${\basename $0} [-s] [-S revs-file] file [ revision ]
+	print STDERR "Usage: ${\basename $0} [-s] [-S revs-file] file [ revision ]
 	-l, --long
 			Show long rev (Defaults off)
 	-t, --time
@@ -23,7 +24,7 @@ ()
 			Use revs from revs-file instead of calling git-rev-list
 	-h, --help
 			This message.
-';
+";
 
 	exit(1);
 }
@@ -35,7 +36,7 @@ ()
 			"help|h" => \$help,
 			"rename|r" => \$rename,
 			"rev-file|S=s" => \$rev_file);
-if (!$rc or $help) {
+if (!$rc or $help or !@ARGV) {
 	usage();
 }