"Every Unix system offers several useful commands for finding
files and searching them for strings. Together with programming
techniques such as streams, pipes, redirections, and regular
expressions they comprise very powerful tools ideal for
"Regular expressions are descriptive patterns dealing with text
strings. They have been part of Unix systems from their beginnings.
They were invented by Mr Ken Thompson, one of Unix's creators.
Regular expressions are very effective tools for processing text
information and they are decidedly worth the effort it takes to
master them, but even a passing familiarity will pay