print "Enter a string: ";
   chomp(my $_ = <STDIN>);

   if ($_ = /([A|a])/) {
       my $afterstring  = $';
       print "This is the after string $afterstring\n";
      if( $afterstring = /([B|b)/ ) {
          print The string has an a  but also a following b\n";
      } else {
          print "The string has an a , but not a following b\n";
      }
    } else {
        print "String did not match\n";
    } 

##</code><code>##

Uncaught exception from user code
        Unmatched [ in regex; marked by <-- HERE in m/([ <-- HERE B|b)/ at Exercise_7_4.pl line 24.