The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

3.14. A Few Sample Regular Expressions

This section presents a small list of regular expressions that might be useful either in actual use or as samples to study. For simplicity, none of these patterns depends on Oniguruma.

3.14.1. Matching an IP Address

Suppose that we want to determine whether a string is a valid IPv4 address. The standard form of such an address is a dotted quad or dotted decimal string. This is, in other words, four decimal numbers separated by periods, each number ranging from 0 to 255.

The pattern given here will do the trick (with a few exceptions such as “127.1”). We break up the pattern a little just for readability. Note that the \d symbol is double-escaped so that the slash in the string gets passed on to the regex. ...