IEEE Standards Interpretations for IEEE Std 1003.2™-1992 IEEE Standard for Information Technology--Portable Operating System Interfaces (POSIX®)--Part 2: Shell and Utilities
Copyright © 1996 by the Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue New York, New York 10016-5997 USA All Rights Reserved.
Interpretations are issued to explain and clarify the intent of a standard and do not constitute an alteration to the original standard. In addition, interpretations are not intended to supply consulting information. Permission is hereby granted to download and print one copy of this document. Individuals seeking permission to reproduce and/or distribute this document in its entirety or portions of this document must contact the IEEE Standards Department for the appropriate license. Use of the information contained in this document is at your own risk.
IEEE Standards Department, Copyrights and Permissions, 445 Hoes Lane, Piscataway, New Jersey 08855-1331, USA
Interpretation Request #137
Topic: Regular Expressions Relevant Sections: 22.214.171.124
Section 126.96.36.199 says: 1785 The ex utility shall support the BREs described in 2.8.3. A null BRE ((//) shall be 1786 equivalent to the last BRE encountered. Historically, however, ex/vi regular expressions have differed from the BRE's described in .8.3 in one respect - they accepted backslash as quoting the following characters within brackets: \, -, ^, and ]. Therefore, the pattern [\^abc] would not historically match \, but only ^, a, b or c. Was it the intention to change ex/vi's regular expressions in this way?
The standard clearly states the requirements for BREs in ex and conforming implementations must conform to this. It is true that historical versions of many utilities had minor varia$$$nts in regular expressions, POSIX.2 regularized most of these utilities including all of the editors to use the standard regular expressions supported by the regular expression standard routines.
Rationale for Interpretation