use strict;
use warnings;

my $fname = 'test.dat';
my $csize = 102400;
my $word = 'bingo';

my ($handle, $length, $end, $pos, $c);

open($handle, $fname);
while () {
    $length = read($handle, $_, $csize);
    if (index($end.$_, $word) != -1) {
        $pos = tell($handle) - $length + index($end.$_, $word) - 100;
        $pos = 0 if $pos < 0;
        seek($handle, $pos, 0);
        read($handle, $_, 220);
        for (@_ = split(/\W+/)) {
            if ($_ eq $word) {
                print join(' ', @_[(($c > 4) ? $c - 5 : 0)..(($c < $#_ - 3) ? $c + 5 : $#_)]);
                last;
            } $c++;
        }
        last;
    }
    last if (!$length);
    ($end) = m/[\W](\w*$)/;
}
close($handle);