We'll be running a number of articles about regular expressions with examples of how they are used. Many programs that were developed under UNIX use regular expressions. It all depends on the program. This general description will be fleshed out with examples in the articles to come.
Regular expressions can find patterns that are much more complicated.
The rules for regular expressions are not terribly complicated. But they tend to use a lot of characters that are special to the UNIX shell. For our first example of using regular expressions, let's consider an email archie search. Using email avoids the complications that accompany running the regular expression through the UNIX shell. We'll be looking at a common class of regular expressions, the case where you're looking for text that contains two known substrings in known order, but with unknown intervening text.