$ perl -le '
> $s = q{</State><Zip>xyz</Zip><Country>US</Country>};
> $s =~ /<Zip>(.*?)<\/Zip>/;
> print qq{Found $1};
> $s = q{No Zip code here};
> $s =~ /<Zip>(.*?)<\/Zip>/;
> print qq{Found $1};'
Found xyz
Found xyz
$