$str = 'a[bdy]dfjaPÑsdafÜ';

while ($str =~ /[^!-~\s]/g)
{
	print "Non ASCII Characater:\t$&\n";
}

Another way:

while ($str =~ /[^[:print:]]/g) 
{
	print "Non Printable Characater:\t$&\n";

}