March 2004 - Posts

• Maintaining monolithic expressions

  I think that it speaks volumes about the readability and maintainability of a regex which is several hundred characters long when it receives 3 comments within 8 hours picking up on errors/improvements. Picking up where I left off yesterday, I'd like Read More... Posted Wednesday, March 31, 2004 9:06 AM by digory | 1 Comments Filed under: Samples

• Using BNF to create Regex's

  While reading the VB Language Spec today I decided to attempt to follow the grammar syntax for matching DateTime Literals: http://msdn.microsoft.com/library/en-us/vbls7/html/vblrfvbspec2_4_6.asp?frame=true DateLiteral ::= # [ Whitespace+ ] DateOrTime Read More... Posted Tuesday, March 30, 2004 2:51 PM by digory | 0 Comments Filed under: Samples

• Know what you're asking for

  Raymond Chen just posted a wonderful reminder about a gotcha when using *? and postfixing it with further matching criteria. http://weblogs.asp.net/oldnewthing/archive/2004/03/25/96456.aspx In a nutshell if you create a pattern like so: <foo.*?>bar</foo> Read More... Posted Friday, March 26, 2004 11:56 AM by digory | 0 Comments Filed under: Samples

• Monolithic regex patterns can cause InvalidProgramException to occur

  Justin blog'ged today about a regex bug which occurs with monolithic patterns ( > 70,000 chars ): http://weblogs.asp.net/justin_rogers/archive/2004/03/21/93459.aspx The wierd part of this bug is that it only manifests itself when using the RegexOptions.Compiled Read More... Posted Monday, March 22, 2004 8:19 AM by digory | 1 Comments Filed under: Samples, Bugs and Suggested Improvements

• Building parsers

  Lately I've been messing around javascript and I've written a simple, generic parser to build parse trees based on a set of configurable rules. Hopefully I'll polish it up and get it posted if I sense any interest in how it's done. Anyways, last night Read More... Posted Friday, March 19, 2004 9:59 AM by digory | 0 Comments Filed under: NYN

• Unlike birds, Character classes do not nest

  While looking through the Character Subtraction spec . the following 2 examples caught my attention: [-[e-f]a-z] Valid, not a subtraction. [a-e[-e-f]] Valid, not a subtraction. This is where it is really useful to have a copy of Regex Coach handy :-) Read More... Posted Thursday, March 18, 2004 8:05 PM by digory | 0 Comments Filed under: Samples

• More about Comment Node syntax/semantics

  Following on from my recent rants surrounding commenting regex's it's worth noting that there are actually 2 valid syntax's for comments: (?#...) syntax (?# matches hello world)he[l]{2}o world #...\n syntax he[l]{2}o world # matches hello world The big Read More... Posted Wednesday, March 17, 2004 9:18 PM by digory | 1 Comments Filed under: Samples

• Some recent RegexLib.com changes

  I've made the following changes to RegexLib.com this week: Quick Search can be performed on a keyword from the Home Page. Patterns can be submitted with whitespace and embedded comments. View and update ratings. 1. Quick Search can be performed on a keyword Read More... Posted Monday, March 15, 2004 9:03 PM by digory | 0 Comments Filed under: RegexLib

• RegexLib.com now supports free-spacing and comments mode

  Tony Stubblebine - author of Regex Pocket Reference - has just blog'ged a post which is a reminder that we should add whitespace to regex's to make them more readable. He's right because, although most of the common regex implementations afford this ability Read More... Posted Sunday, March 14, 2004 9:20 PM by digory | 0 Comments Filed under: RegexLib, Blogs

• Redefining boundaries and lexing through a target string.

  I received an e-mail last week which was asking me for help with a specific problem; the writer wanted a pattern to help filter out spam. They wanted to be able to filter out words which contained more than 2 instances of any "bad characters". Here is Read More... Posted Tuesday, March 09, 2004 5:08 AM by digory | 0 Comments Filed under: Cries for help

• Character Class Subtraction - some more information

  The other day I blog'ged a little bit about Character class subtraction and today I see that the BCL Team have posted a spec. which describes the actual syntax that we can expect to see in the Whidbey bits. CharacterClassSubtraction.doc It's a great initiative Read More... Posted Saturday, March 06, 2004 3:16 PM by digory | 0 Comments Filed under: Samples, Resources

• Regex DateTime validation pattern

  Michael Ash , author of some amazing pattern's has just authored another beauty, a pattern to validate DateTime entries and is supported by both server-side as well as client-side engines: http://www.regexlib.com/REDetails.aspx?regexp_id=610 One of the Read More... Posted Friday, March 05, 2004 9:09 PM by digory | 0 Comments Filed under: RegexLib, Samples

• Character Class subtraction

  I was reading through the XQuery 1.0 and XPath 2.0 Functions and Operators spec tonight, in particular the section relating to: String Function that Use Pattern Matching and, the expanded spec related to the regular expression syntax: XML Schema Part Read More... Posted Thursday, March 04, 2004 7:32 AM by digory | 2 Comments Filed under: NYN

• Mode Modifiers

  I'm always forgetting these things: .Singleline == s .Multiline == m .IgnorePatternWhitespace == x .IgnoreCase == i .ExplicitCapture == n .ECMAScript .RightToLeft .Compiled shorthand can be used as (?s)...(?-s) or, (?smnxi) Share this post: email it! Read More... Posted Tuesday, March 02, 2004 9:28 AM by digory | 0 Comments Filed under: Resources

• How to use FindStr

  Following on from my post yesterday about FindStr.exe I noticed that kayodeok's Weblog have dug up the online link to FindStr documentation, here it is: How to Use Findstr Also contains a link to the entire Command-line reference A-Z list at the bottom Read More... Posted Monday, March 01, 2004 8:57 PM by digory | 1 Comments Filed under: Tools and Sites

• Unicode Regular Expressions

  This is an amazing reference: Unicode Regular Expressions The document fully describes what engines need to do to be Unicode compliant; throughout the course of that they uncover a plethora of useful information nuggets. It also has some excellent links Read More... Posted Monday, March 01, 2004 8:46 PM by digory | 2 Comments Filed under: Resources