regex for port number

A port is a 16-bit unsigned integer ranging from 0 to 65535. The regex pattern tries to figure out if the input string falls under the given range.

A Better approach

Although this works, a far better(and simpler) approach would be this:

1. Take the input string and convert it into a number
2. If possible see if it falls in the range 0-65535
3. If both the conditions succeed, then it is a valid port number