source keyedListLibByReference.tcl

################################################################
# proc address2name {listName address}--
#    resolve an IP address into a name and save it for future use
# Arguments
#   listName	The keyed list of IP addresses and site names
#   address     The IP address to check
# 
# Results
#   The list passed (by name) to this procedure may be modified.
# 
proc address2name {listName address} {
  upvar $listName addrList

  # Try to convert the IP address to a name with the keyed list.
  set name [getValue $addrList $address]
  if {$name eq ""} {
    # If the IP address is not in the list, use nslookup to
    # find the name and save it.

    set txt [exec nslookup $address] 
    set lst [split $txt]

    # Look for line like by searching for list element "name"
    # 50.53.114.66.in-addr.arpa	name = ord-agg-n40.panthercdn.com.

    set pos [lsearch $lst name]
    if {$pos > 0} {
      # If "name" is found, the qualified name is the element after
      # the = - skip 2 to get the name.
      incr pos 2
      set name [lindex $lst $pos]
    } else {
      # If $pos < 0, then there is no name identified, 
      # use the IP address as the resolved name.
      set name $address
    }
    appendKeyedPair addrList $address $name
  }
  return $name
}

set IPList {}
foreach ip {66.114.53.42 72.233.104.123 216.176.180.53 204.176.49.116} {
  address2name IPList $ip
}

foreach {ip addr} $IPList {
  puts "$ip -> $addr"
}