Help with an I-rule rewrite

Thanks for the response. I needed it to work with *.api-np-c.newapps.com and *api-gw-np-a.newapps.com. I got it working with this, finally. I had the endPos wrong initially. It needed to be +8 not +11:

when HTTP_REQUEST {
  if {[HTTP::uri] starts_with "/" } {
    HTTP::uri /[HTTP::host][HTTP::uri]
  }
switch -glob [HTTP::host] {
  "*.api-np-c.regionsapps.com*" {
         set http_host [HTTP::host]
         set startPos [string first .api-np-c $http_host]
         set endPos [expr $startPos + 8]
         set http_host [string replace $http_host $startPos $endPos .api-gw-np-a]
         HTTP::header replace Host "$http_host"
}
  }

}