#!/usr/bin/perl -w
use strict;

open (my $fh1, '<', "testa.txt") or die "cannot open testa";
open (my $fh2, '<', "testb.txt") or die "cannot open testb";

while (   defined (my $test1 = <$fh1>) and 
          defined (my $test2 = <$fh2>)
      )
{
   print "both defined\n";
}