while ($mmap =~ m/^([^\n]*$pat[^\n]\n)/omg)
{
  print $1;
}

##</code><code>##

while ($mmap =~ m/$pat/omg)
{
  my $pos = pos $mmap;
  # Find the beginning and end of this line
  my $first = rindex($mmap,"\n",$pos)+1;
  my $last  = index($mmap,"\n",$pos)+1;
  print substr($mmap,$first,$last-$first);
}

##</code><code>##

#!/usr/bin/perl

use warnings;
use strict;

use Sys::Mmap;

our $pat = shift;

foreach my $a (@ARGV)
{
  my $mmap;
  if (! -f $a)
  {
    warn "'$a' is not a regular file, skipping\n";
    next;
  }
  open(F, "< $a")
    or die "Couldn't open '$a': $!\n";
  mmap($mmap, 0, PROT_READ, MAP_SHARED, F)
    or die "mmap error: $!\n";
  while ($mmap =~ m/^([^\n]*$pat[^\n]\n)/omg)
  {
    print $1;
  }
  munmap($mmap)
    or die "mmunmap error: $!\n";
  close(F)
    or die "Couldn't close '$a': $!\n";
}