"Twice as fast" seems like a lot for in memory operations when there are also disk accesses. I'm sure there are plenty of things to consider (HW, and data size), but with the following code I couldn't get past a difference of around ~5% (although I did notice that trying that with supidly big files made my computer crash :P): 

use v5.20;
use strict;
use warnings;

use Benchmark qw( cmpthese );
use Data::Dump qw( pp );

my $size = 10;
my $length = 1E6;

my @data = ('X' x $length, ) x $size;

sub write_copy 
{
  open my $fh, ">", "tmp.txt" or die "Can't open output file $!";
  $| = 0;
  my $data = shift;
  for (@$data)
  {
    print $fh "$_\n";
  }
}

sub write_simple
{
  local $\ = "\n";
  open my $fh, ">", "tmp.txt" or die "Can't open output file $!";
  $| = 0;
  my $data = shift;
  for (@$data)
  {
    print $fh $_;
  }
}

cmpthese( -15,
          {
            copy => sub { write_copy(\@data); },
            simple => sub { write_simple(\@data); },
          }
        );
__END__
         Rate   copy simple
copy   27.3/s     --    -5%
simple 28.8/s     5%     --

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In reply to Re^4: Write large array to file, very slow by Eily
in thread Write large array to file, very slow by junebob

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