#! perl -slw
use strict;

my $data;
open my $bigFH, '<:raw', 'data/650MB.bin' or die $!;
sysread( $bigFH, $data, -s( 'data/650MB.bin' ) );
close $bigFH;

open my $smallFH, '<', 'data/600.bin' or die $!;
while( <$smallFH> ) {
    print STDERR "\n$. ";
    chomp;
    my $name = "data/$_.posns";
    next if -e $name;
    open O, '>', $name or die $!;
    print STDERR "File: '$name' opened";
    my $p = 0;
    while( $p = 1+index( $data, $_, $p ) ) {
        print O $p;
    }
    close O;
}
close $smallFH;