Here's some code that lets you play with various patterns containing capture groups and also introduces the very useful @- and @+ arrays associated with the capture buffers. Try to explain the output from patterns like  (s(i(l+)y)) and in particular from  (is)|(si) versus  (si)|(is) regexes.

>perl -wMstrict -le
"my $str = 'This is a silly sentence. {3}.';
 REGEX: {
   print 'please enter your pattern: ';
   my $pattern = <STDIN>;
   chomp $pattern;
   last REGEX unless length $pattern;
   if ($str =~ m{$pattern}) {
     print qq{found match for '$pattern'};
     print 'no captures' and redo REGEX unless $#- > 0;
     for my $n (1 .. $#-) {
       my $capture_n = substr $str, $-[$n], $+[$n] - $-[$n];
       print qq{\$$n is '$capture_n'};
       }
     }
   else {
     print qq{NO match found for '$pattern'};
     }
   redo REGEX;
   }
"
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