WG15 Defect Report Ref: 9945-2-125
Topic: Basic Regukar expressions

This is an approved interpretation of 9945-2:1993.


Last update: 1997-05-20



	Topic:                  Basic Regukar expressions
	Relevant Sections:

Defect Report:
	Date: Fri, 19 May 1995 14:40:59 -0700
	From: Greg Burrell <greg@mindcraft.com>

I would like to request an official, binding interpretation from
WG15 concerning the following point in ISO/IEC 9945-2:1993 (POSIX.2).

Section (lines 2994-3010) describe interval expressions in 
Basic Regular Expressions:

	(5) when a BRE matching a single character, a subexpression,
	    or a backreference is followed by an interval expression
	    of the format \{m\}, \{m,\}, or \{m,n\}, it shall match
	    (together with that interval expression) what repeated
	    consecutive occurrences of the BRE would match.  The
	    values of m and n shall be decimal integers in the range

			0 <= m <= {RE_DUP_MAX}

	    where m specifies the exact of minimum number of
	    occurrences and n specifies the maximum number of

When the interval is \{0,0\} what does it mean to match zero occurrences of
the preceding BRE?  Does this mean match the empty string or match the BRE
plus an additional zero occurrences?  For example, 


Will this match before the first 'a' character?  Or will it match the 
entire "abc" portion?  Or will something else occur?

Thank you for your attention to this matter.

Greg Burrell
Mindcraft, Inc.
+1 415 323-9000 x125

Interpretation response

Parentheses are not grouping characters in a BRE.  Assuming that what was 
intended was BRE="\([a-c]*\)\{0,0\}" then a literal reading of the 
text would say that this expression is equivalent to the null regular 
expression.  The meaning of the null regular expression is not specified 
by the standard, and as such no conformance distinction can be made 
between alternative implementations based on this.  This is being referred 
to the sponsor.


Forwarded to Interpretations group: May 28 1995
Proposed resolution forwarded: Aug 11 1995
Finalized: Sept 12 1995