--- a/perlgrok.pl	Wed Sep 29 23:17:35 2021 +0200
+++ b/perlgrok.pl	Thu Sep 30 00:30:07 2021 +0200
@@ -49,7 +49,7 @@
 }
 
 # read patterns
-my $f = new IO::File "< patterns" or die "cannot open patterns: $!";
+my $f = new IO::File "< $fn_pattern" or die "cannot open patterns: $!";
 while( <$f> ) {
     chomp;
     # skip empty and comment lines