Good stuff.. It's faster :-)

#!/usr/local/bin/perl -w
use strict;
use Benchmark;

my $pat = 'foo';

$/=undef;
open F,"<","/usr/share/dict/words";
my $mmap = <F>;
close F;


timethese( 100, {
# 'orig' => sub {
#        while ($mmap =~ m/^([^\n]*$pat[^\n]\n)/omg) {
#            warn $1;
#        }
# },
 'fast' => sub {
         while ($mmap =~ m/\n?(.*$pat.*\n)/omg) {
             warn $1;
        }
 },
 'better' => sub {
     while ($mmap =~ m/(?:\A|\n)(.*$pat.*\n)/omg) {
         warn $1;
     }
 },
}
)
__END__
Benchmark: timing 100 iterations of better, fast...
    better: 26 wallclock secs (23.13 usr +  0.06 sys = 23.19 CPU) @  4
+.31/s (n=100)
      fast: 41 wallclock secs (39.73 usr +  0.09 sys = 39.82 CPU) @  2
+.51/s (n=100)
[download]

(original takes about 25 seconds per iteration on my machine)