iRule Newbie learning - need validation

Actually, I was wrong on this. string trim will remove any instances of individual characters--not just the literal string of "www.". So if your host starts with a w that isn't www., you will get an unintended result:

% string trimleft wily.example.com www.

ily.example.com

Here is a more accurate option using scan:

set host [string tolower [HTTP::host]]
if {[scan $host {www.%s} host_no_www] == 1 }{
   set host $host_no_www
}
log local0. "\$host: $host"

Aaron