Sams Teach Yourself Regular Expressions in 10 Minutes

Lesson 10. Embedding Conditions

A powerful yet infrequently used feature of the regular expression language is the capability to embed conditional processing within an expression. This lesson will explore this topic.

Why Embed Conditions?

[phone] and 123-456-7890 are both acceptable presentation formats for North American phone numbers. 1234567890, (123)-456-7890, and (123-456-7890 all contain the correct number of digits, but are badly formatted. How could you write a regular expression to match only the acceptable formats and not any others?

This is not a trivial problem; consider this obvious solution:

123-456-7890(123)456-7890(123)-456-7890 ...