>perl -wMstrict -le
"my $s = '1a2b3c';
 ;;
 print qq{no /o};
 for my $i (qw(3 2 1)) {
   print qq{matched '$1'} if $s =~ m{ ($i.) }xms;
   }
 ;;
 print qq{with /o};
 for my $i (qw(3 2 1)) {
   print qq{matched '$1'} if $s =~ m{ ($i.) }xmso;
   }
"
no /o
matched '3c'
matched '2b'
matched '1a'
with /o
matched '3c'
matched '3c'
matched '3c'

##</code><code>##

$pattern = 'Seuss';
     while (<>) {
         print if /$pattern/;
     }

##</code><code>##

#!/usr/bin/perl
     #    Improved simple_grep
     $regexp = shift;
     while (<>) {
         print if /$regexp/o;  # a good deal faster
     }