Regex - Overview Go to the next section. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. A regexp r matches a string s if s is in the set of strings described by r .
Some regular expressions match only one string, i.e., the set they describe has only one member.
Other regular expressions match more than one string, i.e., the set they describe has more than one member. To either match or search for a regular expression with the Regex library functions, you must first compile it with a Regex pattern compiling function. A compiled pattern is a regular expression converted to the internal format used by the library functions. Once you've compiled a pattern, you can use it for matching or searching any number of times. Regex provides three groups of functions with which you can operate on regular expressions.