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

for my $string ( '"my" "dog"',
                 '"my" "dog shepherd"',
                 'my dog',
                 'my "dog shepherd"',
                 '"my "dog"',
                 'my "dog shepherd',
               ) {
    my $valid = $string =~ tr/"// % 2 ? 0 : 1;
    print "$valid: $string\n";
}