#!/usr/bin/env perl -l

use strict;
use warnings;
use autodie;

die "Usage: $0 file1 file2\n" unless @ARGV == 2;

my (@fhs, $shorter);

for (@ARGV) {
    die "'$_' is zero-length\n" if -z;
    open my $fh, '<', $_;
    push @fhs, $fh;
}

LOOP: while (1) {
    my @out_line;

    for (0 .. 1) {
        my $line = readline $fhs[$_];

        if (! defined $line) {
            $shorter = $_ unless defined $shorter;
            last LOOP if $shorter != $_;
            seek $fhs[$_], 0, 0;
            $line = readline $fhs[$_];
        }

        push @out_line, $line;
    }

    chomp @out_line;
    print @out_line;
}