Date:         Tue, 16 Oct 2001 22:07:42 -0000
Reply-To:     David Wall <darkon@ONE.NET>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         David Wall <darkon@ONE.NET>
Organization: Posted via Supernews, http://www.supernews.com
Subject:      Re: Resolving an IP-address

I wrote:
>                                   Since all you want to do is turn IPs
> into DNS, write one simple (non-SAS) program that reads an input
> (text) file with IP addresses, one per line, resolves the DNS name,
> and creates an output file with the IP address and DNS name on the
> same line.  Then have SAS get the IPs, write them to a text file, use
> x to execute the little non-SAS program, then have SAS read in the IP
> and DNS from the output file.  I'd write the non-SAS part in Perl,
> since it has tools that make this kind of thing easy, but you could
> use C or whatever.

Here's a short Perl program to do what I said above:

#!/usr/bin/perl
use strict;
use warnings;
use Socket;

my $in  = 'ip-addresses'; # input:  file containing IPs, one per line
my $out = 'ip-dns';       # output: ip and dns name

open IN,  "$in"   or die "Error opening $in:  $!";
open OUT, ">$out" or die "Error opening $out: $!";
while (<IN>) {
    chomp;
    my $ip  = inet_aton $_;
    my $dns = gethostbyaddr $ip, AF_INET;
    print OUT "$_ $dns\n";
}

Note that this will not necessarily get you the hostname you expect.  I
pinged www.yahoo.com to get an IP address for testing, but when I used
that IP to get a hostname, I got back w5.dcx.yahoo.com.

--
David Wall
darkon@one.net