sub is_digits {
    my @rv = $_[0] =~ /^([0-9]+)$/;
    return @rv[ 0 .. $#rv ];
}
my $nothing = is_digits('abc');
my @arr1 = ($nothing);
my @arr2 = ('some', 'thing');
push @arr2, @arr1;
print "There are ", scalar(@arr2), " elements in \@arr2\n";
print '$arr2[2] is ', defined($arr2[2])?'':'un', "defined\n";