#!/usr/bin/perl

use strict;
use warnings;

open my $fh, '<', shift or die "Error: $!";

my $chunk;
my $find = 'regf';
while (my $bytes = read $fh, $chunk, 1024)
{
    unless ((my $idx = index $chunk, $find) < 0)
    {
        printf "Found %s at offset %x\n", $find, tell $fh + $idx - $bytes;
    }
}