regular expression library for C++ This package forms part of the Boost C++ Libraries collection. Regular expressions are a form of pattern-matching that are often used in text processing; many users will be familiar with the Unix utilities grep, sed and awk, and the programming language perl, each of which make extensive use of regular expressions. Traditionally C++ users have been limited to the POSIX C APIs for manipulating regular expressions, and while regex does provide these APIs, they do not represent the best way to use the library. For example regex can cope with wide character strings, or search and replace operations (in a manner analogous to either sed or perl), something that traditional C libraries can not do.