Procmail implements a form of regular expressions that operates slightly differently to other UNIX utilities. Here we cover the basic differences and guide the new user into the powerful world of Regular Expressions, their meanings, implementations, and uses.
We have already seen that Procmail matches are case insensitive unless the
D flag is used. This is also true for regular expressions. Procmail also uses multiline matches by default.
If you are new to the world of Linux and programming in general, you could well have escaped the powerful features that Regular Expressions bring to processing data. In its simplest form, Regular Expressions can be understood as searching for a phrase or ...