use strict;
use warnings;
use Tie::File;
use Getopt::Std;

our %opts;
getopt('AB',\%opts);
die "USAGE: $0 [-An] [-Bn] match file" unless @ARGV;
my ($match,$filename) = @ARGV;

my @file;
tie @file, 'Tie::File', $filename;

# i wish there was a way for grep to return indices ...
my @found;
for (0..$#file) {
   push @found, $_ if $file[$_] =~ /$match/;
}

for (@found) {
   my ($start,$end) = ($_,$_);

   $start -= $opts{A} if $opts{A};
   $end   += $opts{B} if $opts{B};
 
   $start = 0 if $start < 0;
   $end = $#file if $end > $#file;

   print $_,$/ for @file[$start..$end];
}