one of the documented procedures in this installation of the ACS
util_get_http_status   url   { use_get_p "1" }   { timeout "30" }
What it does:
Returns the HTTP status code, e.g., 200 for a normal response or 500 for an error, of a URL. By default this uses the GET method instead of HEAD since not all servers will respond properly to a HEAD request even when the URL is perfectly valid. Note that this means AOLserver may be sucking down a lot of bits that it doesn't need.
Defined in: /web/philip/packages/acs-core/utilities-procs.tcl

Source code:

    if $use_get_p {
	set http [ns_httpopen GET $url "" $timeout] 
    } else {
	set http [ns_httpopen HEAD $url "" $timeout] 
    # philg changed these to close BOTH rfd and wfd
    set rfd [lindex $http 0] 
    set wfd [lindex $http 1] 
    close $rfd
    close $wfd
    set headers [lindex $http 2] 
    set response [ns_set name $headers] 
    set status [lindex $response 1] 
    ns_set free $headers
    return $status