$string might be a phone number: 99999999999999999999999999       # see Note 2
$string2 might be a phone number: 9-999-999-999-999-999-999-999-9999 # also see Note 2
stiller's snippet:
999999999.000000  # a float, as stiller noted, this address's OP's problem,
999999999         # whereas, Perl makes it easy to use this as a string