On 18 April, bill parducci writes: [xacml] regular expressions - subgroup follow-up > regular expressions are acknowledged as being tied to the POSIX (IEEE) > standard. i suggest that we consider basic regular expresssions (BRE) as > defined in POSIX specification 2: > >
http://www.opengroup.org/onlinepubs/007908799/xbd/re.html#tag_007_003 > > there is also an exteded regular expression set: > >
http://www.opengroup.org/onlinepubs/007908799/xbd/re.html#tag_007_004 > > have not really looked through it to discover the differences. I think I would vote for ERE, due to the " " metacharacter (RE1 RE2) matches RE1 OR RE2, but I don't have a strong preference either way. "ed", "grep" use BRE. "egrep", "awk" use ERE. Both BRE and ERE support: . : matches any single character [xyz] : matches 'x' or 'y' or 'z' [x-z] : matches any character in the range 'x' - 'z' (RE)* : matches 0 or more occurrences of RE (must be (RE)* in BRE) [:class:] : matches any character in the specified character "class", where "class" can be: alnum - alpha or numeric alpha - alpha blank - blank cntrl - control char digit - 0-9 lower - lower-case alpha upper - upper-case alpha etc. [^xyz] : matches any character except 'x' or 'y' or 'z' [^x-z] : matches any character except one in the range 'x' - 'z' ERE supports the following metacharacters not supported by BRE: + : matches 1 or more occurrences of the preceding RE ? : matches 0 or 1 occurrences of the preceding RE : specifies that either the preceding or following RE can be matched ERE supports anchoring (^ - beginning of line; $ - end of line) in subexpressions. BRE supports anchoring only at beginning or end of the entire expression. ERE does not support "back references":
= the nth preceding subexpression enclosed in (RE). Both BREs and ERE's are supported by the UNIX Regular Expression Matching interfaces "regcomp(3C)" and "regexec(3C)". Anne -- Anne H. Anderson Email:
Anne.Anderson@Sun.COM Sun Microsystems Laboratories 1 Network Drive,UBUR02-311 Tel: 781/442-0928 Burlington, MA 01803-0902 USA Fax: 781/442-1692