#!/usr/bin/env perl

use strict;
use warnings;
use Benchmark qw ( :hireswallclock cmpthese timethese );

our $file   = qq (huge.file);
our $amount = 1_000_000;

sub karl {
    our ( $file, $amount );
    open( my $in, "<", $file );
    while (<$in>) {
        next if $. <= $amount;
        1;
    }
    close $in;
}

sub laurent {
    our ( $file, $amount );
    open( my $in, "<", $file );
    my $useless_header_line = <$in> for 1 .. $amount;
    while (<$in>) {
        1;
    }
    close $in;
}

my $results = timethese(
    10,
    {
        'karlgoethebier' => 'karl',
        'Laurent_R'      => 'laurent',
    }
);

cmpthese($results);

__END__

karls-mac-mini:monks karl$ perl -e 'print qq(Lorem ipsum kizuaheli\n) for 1..50_000_000;' > huge.file

karl-mac-mini:monks karl$ ls -hl huge.file 
-rw-r--r--  1 karl  karl   1,0G 21 Feb 17:24 huge.file

karls-mac-mini:monks karl$ wc -l huge.file 
 50000000 huge.file

karls-mac-mini:monks karl$ ./1117372.pl
    Benchmark: timing 10 iterations of Laurent_R, karlgoethebier...
    Laurent_R: 65.9521 wallclock secs (63.43 usr +  2.34 sys = 65.77 CPU) @  0.15/s (n=10)
    karlgoethebier: 127.837 wallclock secs (124.90 usr +  2.55 sys = 127.45 CPU) @  0.08/s (n=10)
               s/iter karlgoethebier      Laurent_R
karlgoethebier   12.7             --           -48%
Laurent_R        6.58            94%             --