__Perl Compatible Regular Expressions__ (__PCRE__) is a library (computing) written in C (programming language), which implements a regular expression engine, inspired by the capabilities of the Perl. Philip Hazel started writing PCRE in summer 1997. PCRE's syntax is much more powerful and flexible than either of the regular expression#POSIX flavors and than that of many other regular-expression libraries.
While PCRE originally aimed at feature-equivalence with Perl, the two implementations are not fully equivalent. During the PCRE 7.x and Perl 5.9.x phase, the two projects have coordinated development, with features being ported between them in both directions.
A number of prominent open-source programs, such as the Apache HTTP Server and Nginx HTTP Servers, and the PHP and R (programming language) scripting languages, incorporate the PCRE library; proprietary software can do likewise, as the library is BSD licensed. As of Perl 5.10, PCRE is also available as a replacement for Perl's default regular expression engine through the <code>re::engine::PCRE</code> module.
The library can be built on Unix, Windows, and several other environments. PCRE is distributed with a POSIX C wrapper, a native C++ wrapper, several test programs, and the utility program <tt>pcregrep</tt> built in tandem with the library.
# See also
- Perl Compatible Regular Expressions - PCRE - Regular expression - Comparison of regular expression engines
- https://www.regextranslator.com/ - http://rick.measham.id.au/paste/explain.pl
- PCRE manual at - pcre.org 
- Test expressions at - regextester.com
- Library - regexlib.com