pcregrep 2:8.39-8~build1 (amd64 binary) in ubuntu bionic

 Perl-style regexps have many useful features that the standard POSIX ones
 don't; this is basically the same as grep but with the different
 regexp syntax.
 .
 The other reason for the existence of pcregrep is that its source code is an
 example of programming with libpcre.