Regular Expression for validating DNS label ( host name)

Question

I would like to validate a hostname using only regualr expression.

Host Names (or \'labels\' in DNS jargon) were traditionally defined by RFC 952 and RFC 1123 and m

Answer 1

^(?![0-9]+$)(?!-)[a-zA-Z0-9-]{,63}(?

I used the following testbed written in Python to verify that it works correctly:

tests = [
    ('01010', False),
    ('abc', True),
    ('A0c', True),
    ('A0c-', False),
    ('-A0c', False),
    ('A-0c', True),
    ('o123456701234567012345670123456701234567012345670123456701234567', False),
    ('o12345670123456701234567012345670123456701234567012345670123456', True),
    ('', True),
    ('a', True),
    ('0--0', True),
]

import re
regex = re.compile('^(?![0-9]+$)(?!-)[a-zA-Z0-9-]{,63}(?