perl -wle"for ('00001'..'10000') { print join ' ', ($_) x 20; }" > temp.tmp

##</code><code>##

  open my $fh, 'temp.tmp' or die $!;

  # Alternative 1: 40 984 K
  my @temp = map { "$_\n" } map { split ' ' } <$fh>;

  # Alternative 2: 29 076 K
  my @temp = map { split ' ' } <$fh>;
  $_ .= "\n" for @temp;

  # Alternative 3: 14 816 K
  local $_;
  my @temp;
  push @temp => map "$_\n", split ' ' while <$fh>;