This post originated from an RSS feed registered with .NET Buzz by Scott Watermasysk. Original Post: The Perverse Art of Regular Expressions Feed Title: ScottW's ASP.NET WebLog Feed URL: /error.aspx?aspxerrorpath=/blog/rss.aspx Feed Description: ASP.NET and Blogging Latest .NET Buzz Posts Latest .NET Buzz Posts by Scott Watermasysk Latest Posts From ScottW's ASP.NET WebLog

For those of you who have not seen the .Text code, no ASPX pages exist except for the admin section. All of the blog pages are built on the fly. To decide which page to load, I have a custom set of HttpHandlers/HttpHandlerFactories.

A set of configurable Regular Expressions controls which Handler/Factory to load. I had kept my expressions rather simple, but as more and more blogs are created, I am noticing a need to extend some of the expressions.

Two items I neglected from my original patterns are "." and spaces. Space's will come later. We can focus on "." now.

Earlier today Donny IMed me saying his latest .Text update killed all blogs on DNJ with a "." in the blog name.

In short, I needed a Regular Expression that matched the following cases:

/Directory/Blog
/Directory/Blog/
/Directory/Blog/default.aspx

/Directory/Blog.Blog
/Directory/Blog.Blog/
/Directory/Blog.Blog/default.aspx

I also needed the expression not to match the following three cases:

/Directory
/Directory/
/Directory/default.aspx

A quick post to the ASPAdvice Regex List resulted in a couple of great suggestions.

The simplest and quickest seems to be by Wayne King:

If you simply want to verify that the string does not end with '.aspx', this will do that:

  $(?<!\.aspx)

If you want to verify there are exactly two directories specified, you can add to it to get:

  ^(/[\w.]+){2}.*$(?<!\.aspx)

A pattern that works precisely as you ask, "say \w|\. and NOT .aspx" is:

  \w|\.(?!aspx)

Which can be used to compose an alternate overall pattern that verifies there are exactly two directories:

  ^(/(\w+|\.(?!aspx))+){2}(/|/default\.aspx)?$

A huge thanks goes out to Wayne, Darren, and all of the others who quickly responded.