Mastering Windows PowerShell Scripting - Third Edition

IP addresses

Validating an IPv4 address using a regular expression is not necessarily a trivial task.

The IP address consists of four octets; each octet can be a value between 0 and 255. When using a regular expression, the values are considered strings, therefore, the following strings must be considered:

• [0-9]: 0 to 9
• [1-9][0-9]: 1 to 9, then 0 to 9 (10 to 99)
• 1[0-9]{2}: 1, then 0 to 9, then 0 to 9 (100 to 199)
• 2[0-4][0-9]: 2, then 0 to 4, then 0 to 9 (200 to 249)
• 25[0-5]: 2, then 5, then 0 to 5 (250 to 255)

Each of these is an exclusive set, so alternation is used to merge all of the previous small expressions into a single expression. This generates the following group, that matches a single octet (0 to 255):

([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]) ...