Logging Certain number of characters with HTTP::request

I think you can get what you're looking for by combining a few pre-built commands rather than doing some complicated scan or regular expression.

Check out these commands:

HTTP::method - http://devcentral.f5.com/wiki/default.aspx/iRules/HTTP__method.html

HTTP::uri - http://devcentral.f5.com/wiki/default.aspx/iRules/HTTP__uri.html

and

IP::client_addr - http://devcentral.f5.com/wiki/default.aspx/iRules/IP__client_addr.html,

If you put these three together I think you can achieve 100% of what you're looking for easily and for very few cycles.

Something like this:

when HTTP_REQUEST {
  log local0. "Client Address:[IP::client_addr], Request Type:[HTTP::method], Request URI:[HTTP::uri]"
} 

Simple, but it should get you where you want to go, unless there's something specific in the header past those pieces of information that you want.

Colin