how to use switch to match datagroup

The value for [HTTP::path] is cached in memory the first time the command is run. However, if you perform an operation on the path, like [string tolower [HTTP::path]] that output is not cached. So in your example, if you're running [HTTP::path] multiple times, it's better to not save the value to a variable.

If you were checking the path set to lower case in multiple locations in the iRule, it would be more efficient to save the value to a variable versus running string tolower more than once.

Here are examples of the two different scenarios. I hope this is clearer for you.

 Example using no variable as [HTTP::path] is cached:
switch -glob [HTTP::path] {
    "*gif" -
    "*png" {
        switch -glob [HTTP::path] {
            "/static.*" -
            "/s.*" {
                switch -glob [HTTP::path] {
                    "*cswebtool*" -
                    "*cobrands*" {
                        persist none
                        pool SRWD52-STATIC
                        return
                    }
                }
            }
        }
    }
}

Or

 Example using a variable as [string tolower [HTTP::path]] is not cached:
set path [string tolower [HTTP::path]]
switch -glob $path {
    "*gif" -
    "*png" {
        switch -glob $path {
            "/static.*" -
            "/s.*" {
                switch -glob $path {
                    "*cswebtool*" -
                    "*cobrands*" {
                        persist none
                        pool SRWD52-STATIC
                        return
                    }
                }
            }
        }
    }
}

Aaron