Regex and extended regex

Authors:
Cezar Câmpeanu;Kai Salomaa;Sheng Yu
Affiliations:
Department of Mathematics and Computer Science, UPEI, Charlottetown, PE;Computing and Information Science Department, Queen's University, Kingston, Ontario, Canada;Department of Computer Science, University of Western Ontario, London, Ontario, Canada
Venue:
CIAA'02 Proceedings of the 7th international conference on Implementation and application of automata
Year:
2002

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Abstract

Regex are used in many programs such as Perl, Awk, Python, egrep, vi, emacs etc. It is known that regex are different from regular expressions. In this paper, we give regex a formal treatment. We make a distinction between regex and extended regex; while regex present regular languages, extended regex present a family of languages larger than regular languages. We prove a pumping lemma for the languages expressed by extended regex. We show that the languages represented by extended regex are incomparable with context-free languages and a proper subset of context-sensitive languages.