fix match drawing if match group doesn't start at the beginning

Also display an error message if a regex doesn't contain a match group.

diff --git a/bin/fcscs b/bin/fcscs
index 0033af86f8eeb10be82aa8c27fa81ee2cb019854..abe9712ea3449e2383933df563a59064144679ee 100755 (executable)
--- a/bin/fcscs
+++ b/bin/fcscs
@@ -385,8 +385,11 @@ sub get_regex_matches {
 
     my @matches;
     while ($input->{string} =~ /$regex/g) {
+        my $offset = $-[1];
+        die "Match group required in regex '$regex'" if not defined $offset;
+
         my ($x, $y) = input_match_offset_to_coordinates($input->{width},
-                                                        $-[0]);
+                                                        $offset);
         push @matches, { x => $x, y => $y, string => $1 };
     }
     return @matches;