#!/bin/sh
#
# iptoname 1.00
# by Adam M. Costello
# <amc@cs.wustl.edu>

[ $# -eq 1 ] || {
  echo "usage:" >&2
  echo "`basename $0` <address>" >&2
  exit 1
}

oldIFS=$IFS
IFS=.$oldIFS
set -- $1
IFS=$oldIFS

if [ -x /usr/sbin/nslookup ]; then
  nslookup=/usr/sbin/nslookup
elif [ -x /usr/etc/nslookup ]; then
  nslookup=/usr/etc/nslookup
else
  nslookup=nslookup
fi

addr=$4.$3.$2.$1.in-addr.arpa

name=`
  { echo "set querytype=ptr";
    echo "$addr";
  } | $nslookup 2>&1 |
    awk '
      $1 == "'"$addr"'" {
        for (i = 2;  i <= NF - 2;  ++i)
          if ($i == "name" && $(i+1) == "=") print $(i+2)
      }
    '
`

[ -n "$name" ] && echo "$name"