Regular expressions are powerful tools for selecting particular lines from files or output. A lot of UNIX commands use regular expressions: vim, perl, the PostgreSQL database and so on. They can be made available in any language or application using external libraries, and they even found their way to non-UNIX systems. For instance, regular expressions are used in the Excell spreadsheet that comes with the MicroSoft Windows Office suite. In this chapter we got the feel of the grep command, which is indispensable in any UNIX environment.
The grep command can do much more than the few tasks we discussed here; we only used it as an example for regular expressions. The GNU grep version comes with plenty of documentation, which you are strongly advised to read!
Bash has built-in features for matching patterns and can recognize character classes and ranges.