Beginning with PHP 4.2.0 these functions are enabled by default. You can
disable the pcre functions with
--without-pcre-regex. Use
--with-pcre-regex=DIR to specify DIR
where PCRE's include and library files are located, if not using bundled library.
For older versions you have to configure and compile PHP
with --with-pcre-regex[=DIR] in order
to use these functions.
The Windows version of PHP has built-in
support for this extension. You do not need to load any additional
extensions in order to use these functions.
Note:
As of PHP 5.3.0 this extension cannot be disabled and is therefore always
present.
It is still possible to build against an external PCRE library by using
--with-pcre-regex=DIR