regex in iRules

The answer to your question is yes, you can use regex's when needed. This can be done with the regexp command or the -regex option for switch. But, with that being said, I would highly suggest trying to find alternate ways to do things like this without full blown regular expressions.

Your example of allowing "/site1*" but not "//site1*" is actually what your iRule above is doing. You are specifying to start a string with "/site1" and allow anything after that initial string. Since "//site1*" doesn't start with "/site1" then it will not pass through. Am I missing something here?

The -glob option in the switch command, as well as the "string match" command are great options for using a wildcard or range of characters without the need for the full blown regex engine.

Now, if you really want to reject all other requests not starting with "/site1" then you might want to add a default clause in your switch statement and explicitly issue a reject statement in there.

 when HTTP_REQUEST {  
   switch -glob [string tolower [HTTP::uri]] {  
     "/site1*" -  
     "/site2*" -  
     "/site3*" -  
     "/site4*" {  
       pool Test_Pool  
     } 
     default { 
       reject 
     }  
   }  
 }

Let me know if I'm missing anything or you need more clarification or examples and I'll be glad to help.

-Joe