A regular expression (or regexp, or pattern) is a text string that describes some set of strings.
Using the Regex library, you can:
- see if a string matches a specified pattern as a whole, and
-search within a string for a substring matching a specified pattern.
Regex provides three groups of functions with which you can operate on regular expressions. One group--the GNU group--is more powerful but not completely compatible with the other two, namely the POSIX and Berkeley UNIX groups; its interface was designed specifically for GNU. The other groups have the same interfaces as do the regular expression functions in POSIX and Berkeley UNIX.