Mastering Windows PowerShell Scripting - Third Edition

Repeating groups

Groups may be repeated using any of the quantifiers. The regular expression that tentatively identifies an IP address can be improved using a repeated group. The starting point for this expression is as follows:

[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+ 

In this expression, the [0-9]+ term followed by a literal . character is repeated three times. Therefore, the expression can become as follows:

([0-9]+\.){3}[0-9]+ 

The expression itself is not very specific—it will match much more than an IP address, but is also now more concise. This example will be taken further later in this chapter.

If * is used as the quantifier for the group, it becomes optional. If faced with a set of version numbers ranging in formats from 1 to 1.2.3.4, a similar ...