redirect http://domain.com to http://www.domain.com

The command that you're looking for is HTTP::redirect.

You would use this like:

when HTTP_REQUEST {
  if {[HTTP::host] eq "domain.com" } {
    HTTP::redirect "http://www.domain.com"
  }
}

You can read more about this, and other iRules commands in the manual, here: Click here

-Colin