open ONE, '<' ,'one.txt';
open TWO, '<' ,'two.txt';

my $finished_1, $finished_2;

until ( $finished_1 and $finished_2) {
   my $line1 = <ONE>;
   my $line2 = <TWO>;
   chomp $line1, $line2;

   print "$line1 \t $line2";

   ++$finished_1, seek ONE,0,0 if eof ONE;
   ++$finished_2, seek TWO,0,0 if eof TWO;
}

##</code><code>##

1 	 1
2 	 2
1 	 3
2 	 4
1 	 5