use strict;
use Tie::File;
my @file;
my $filename = 'test.txt';
tie @file, 'Tie::File', $filename
  or die "Couldn't open '$filename' : $!\n";

die "The second line in '$filename' is not blank !\n"
  unless $file[1] eq '';

# Remove first line :
shift @file;

# Remove second line :
shift @file;

# Replace first (former third) line :
$file[0] = "New text";