Zip Lines

#!/usr/bin/perl
use strict;
use warnings;
use utf8;
use open qw|:std :encoding(utf8)|;
use feature qq|say|;

open my $f, '<', shift @ARGV or die;
my @lines1 = <$f> if defined $f;
undef $f;
open $f, '<', shift @ARGV or die;
my @lines2 = <$f> if defined $f;
undef $f;

while (@lines1 or @lines2) {
  print shift @lines1 if @lines1;
  print shift @lines2 if @lines2;
  say '';
}