test_pre.pl:
use strict;

open(DATA, ">", "test.dat");
foreach (1..$ARGV[0]) {
    print DATA "$_\n";
}
close(DATA);

##</code><code>##

test_slurp.pl:
use strict;

use constant SIZE => 10000;

my $t0 = time();
my $lines = read_log_s();
my @data = (0..SIZE - 1);
foreach my $line (@{$lines}) {
    $line += ($data[$line % SIZE] - $data[($line + 1) % SIZE]);
}
print "Used ", time() - $t0, "\n";

sub read_log_s {
    local $/;
    open(FILE, "<", "test.dat");
    my @lines = split /\n/, <FILE>;
    close(FILE);
    return \@lines;
}

test.pl:
use strict;

use constant SIZE => 10000;

my $t0 = time();
my @data = (0..SIZE - 1);
open(FILE, "<", "test.dat");
my $line;
while ($line = <FILE>) {
    $line += ($data[$line % SIZE] - $data[($line + 1) % SIZE]);
}
close(FILE);
print "Used ", time() - $t0, "\n";