#! /usr/bin/env perl
use strict;
use warnings;
use 5.010;

my @array1 = qw(
    1
    1
    1
    0
);

my @array2 = qw(
    2
    2
    2
    2
);
$array2[-2]= undef;


for( my $i=0;$i<@array2; $i++ ) {

    next if !defined $array2[$i] || 0 == length($array2[$i]);

    $array1[$i] = $array2[$i]   if $array1[$i] < $array2[$i];
}

say $_ for @array1;

__END__