use strict;
use warnings;

my $file1 = make_func (shift);
my $file2 = make_func (shift);

my ($line1, $line2);
chomp $line1 and print $line1, $line2 while ($line1 = $file1->() and $line2 = $file2->());

sub make_func {
	my $file = shift;
	open my $FH, "<", $file or die "could not open $file $!";
	sub {<$FH>; }
}