RegularExpressions

• a string whose pattern describes a set of strings.
• is a set of characters (string) that specify a pattern.

• OgreKit - framework
• RegExHelp - general discussion, Q-and-A

References:

• The re_format(7) man page. [http://developer.apple.com/documentation/Darwin/Reference/ManPages/man7/re_format.7.html]
• Mastering Regular Expressions, 2nd Edition [http://www.oreilly.com/catalog/regex2/]
• Regular Expressions: [http://www.grymoire.com/Unix/Regular.html]
• GNU grep: [http://www.gnu.org/software/grep/doc/grep.html]
• Regular Expression HOWTO [http://py-howto.sourceforge.net/regex/regex.html]
• Five Habits for Successful Regular Expressions: [http://www.oreillynet.com/pub/a/onlamp/2003/08/21/regexp.html] German version: [http://www.oreilly.de/catalog/regex2ger/index.html]
• Regular expressions simplify pattern-matching code: [http://www.javaworld.com/javaworld/jw-02-2003/jw-0207-java101.html]
• International Components for Unicode [http://icu-project.org/userguide/regexp.html]

Software:

• ObjPCRE ( http://sourceforge.net/projects/objpcre ) is a well documented PCRE wrapper written in 100% Objective-C/C. It can be easily implemented into any Cocoa application. Does not appear to support extracting groups from a matched string. (MIT License)
• AGRegEx ( http://sourceforge.net/projects/agkit ) is an OO wrapper for PCRE -- works great
• MOKit's Regular expression: http://www.lorax.com/FreeStuff/MOKit.html
• OFRegularExpression (part of the OmniFoundation Kit)
• OgreKit (OniGuruma? Regular Expression Framework for Cocoa): http://www8.ocn.ne.jp/%7esonoisa/OgreKit/index.htm
• PCRE, as used in many software packages, including PHP. [http://pcre.org/]
• regex(3) - the regular expression library built into Darwin/Mac OS X. [http://developer.apple.com/documentation/Darwin/Reference/ManPages/man3/regex.3.html]
• CSRegex - Objective-C wrapper for the libc functions above -- simple and easy to include in projects.
• REtry? - showing use of MOKit [http://deallus.com/retry.shtml]
• RegexKit - PCRE based regular expressions. Excellent documentation [http://regexkit.sourceforge.net/]
• CocoaOniguruma - a simple and tiny binding of Oniguruma

I have looked into a few RegularExpressions libraries for use in my program, but all the ones I have used are rather slow. I've resorted to my original way of piping data to a Perl script which handles the regular expressions and returns it back:

#!/usr/bin/perl
# script for removing HTML
$str = "";
while ($line=<STDIN>)
{
	$str .= $line;
}
$str =~ s/<(?:[^>'"]*|(['"]).*?)*>//gsi;
print $str;

Maybe not as easy to work with, but you could use flex to generate the scanner (I _think_ the experimental C++ output is thread safe). There are tools similar to flex, i.e. which generate a DFA-based matcher, and thus are much faster than the misc. regexp libraries -- as for libraries, perl is probably the most optimized one!

P.S. To do the above (with perl) you can call (can't disable the italic, so view source):

perl -pe 's/<(?:[^>'\"]*|(['\"]).*?)*>//gsi'

I don't know if it's any faster than what you've already tried, or even usable, but NSString has some undocumented regexp functions.