Programming Forums > Script Programming > Bash / Shell Scripting

a thing · Sep 27th, 2006, 11:25 PM

How could I check if a DNS domain exists? dig doesn't work because my DNS servers (OpenDNS) return the IP of their search server.

jim mcnamara · Sep 28th, 2006, 3:27 PM

Do you want to check the existence of any domain - nslookup?
Options let you specify a domain to limit the search. You can also specify the
DNS box.

I'm not sure what you meant by a DNS domain in this context....

a thing · Sep 28th, 2006, 6:34 PM

nslookup isn't what I want, but its man page pointed me to host, which is exactly what I wanted.

a thing · Sep 29th, 2006, 12:54 AM

:/ host doesn't handle LAN IPs or aliases in /etc/hosts.

sarumont · Sep 29th, 2006, 12:19 PM

Check out 'man gethostbyname'. I believe that this library uses the standard DNS lookup stack in *nix (typically in /etc/host.conf).

a thing · Sep 29th, 2006, 6:50 PM

Umm... this is the shell forum, not the C forum.

sarumont · Oct 3rd, 2006, 10:11 AM

Quote:

Originally Posted by a thing

Umm... this is the shell forum, not the C forum.

If the problem cannot be solved with existing shell tools, then you may need to write your own.

If you just simply want to see if a domain name resolves, you can use something like:

(Toggle Plain Text)

ping $DOMAIN -c1 | grep ^PING | \
awk -F\  '{ gsub( /\(/,// , $3); gsub( /\)/,//,$3 ); print $3 }'

That returns the IP address of the domain. If the domain does not resolve, you get:

(Toggle Plain Text)

ping: unknown host googlaoeuaoee.com

If you do not care what the IP is, you can simply use ping:

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#!/bin/bash

ping -c1 $1 >> /dev/null

if [ $? == 2 ]; then
    echo "$1 does not exist."
else
    echo "$1 exists."
fi

Hope this helps.

a thing · Oct 3rd, 2006, 8:11 PM

Quote:

Originally Posted by me

my DNS servers (OpenDNS) return the IP of their search server

(Toggle Plain Text)

notroot@arthur[0:~]$ ping -c1 asdr.ear.baawer
PING asdr.ear.baawer (208.67.219.40) 56(84) bytes of data.
64 bytes from ip-208-67-219-40.n.opendns.com (208.67.219.40): icmp_seq=1 ttl=50 time=14.1 ms

--- asdr.ear.baawer ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 14.197/14.197/14.197/0.000 ms
notroot@arthur[0:~]$ echo $?
0
notroot@arthur[0:~]$

sarumont · Oct 3rd, 2006, 10:17 PM

Quote:

Originally Posted by a thing

(Toggle Plain Text)

notroot@arthur[0:~]$ ping -c1 asdr.ear.baawer
PING asdr.ear.baawer (208.67.219.40) 56(84) bytes of data.
64 bytes from ip-208-67-219-40.n.opendns.com (208.67.219.40): icmp_seq=1 ttl=50 time=14.1 ms

--- asdr.ear.baawer ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 14.197/14.197/14.197/0.000 ms
notroot@arthur[0:~]$ echo $?
0
notroot@arthur[0:~]$

That clears things up a bit. Whether the domain exists or not has no bearing on OpenDNS's reply. That is quite crappy. Short of using your own DNS servers (or your ISP's), putting two and two together should work for you:

-'host' can resolve the IP of any FQDN given it
-'ping' can resolve the IP of any local DN (that you may specify in /etc/hosts)

host + ping + glue = solution

Edit:

Playing around a bit more with OpenDNS as my nameserver, it appears to only return its search server IPs when the domain is not found. This being the case, you can still solve this with one tool (ping) and some parsing of the results (if $IP is in $IPS_OWNED_BY_OPENDNS....).

a thing · Oct 3rd, 2006, 10:38 PM

Your proposed solution has given me a better idea. Ping gives the packet loss percent. All I need to do is check if that's like <=15.

Damn I should learn awk.

Sep 27th, 2006, 11:25 PM	#1
a thing Unverified User Join Date: Aug 2005 Location: none Posts: 146 Rep Power: 0	domain existence How could I check if a DNS domain exists? dig doesn't work because my DNS servers (OpenDNS) return the IP of their search server. __________________ Warning: My posts may change (dramatically) within the first 15 minutes they're posted. Got 'Nux?�GNU/Linux and other free software support. It's GNU/Linux, not just Linux.

Sep 28th, 2006, 6:34 PM	#3
a thing Unverified User Join Date: Aug 2005 Location: none Posts: 146 Rep Power: 0	nslookup isn't what I want, but its man page pointed me to host, which is exactly what I wanted. __________________ Warning: My posts may change (dramatically) within the first 15 minutes they're posted. Got 'Nux?�GNU/Linux and other free software support. It's GNU/Linux, not just Linux.

Sep 29th, 2006, 12:54 AM	#4
a thing Unverified User Join Date: Aug 2005 Location: none Posts: 146 Rep Power: 0	:/ host doesn't handle LAN IPs or aliases in /etc/hosts. __________________ Warning: My posts may change (dramatically) within the first 15 minutes they're posted. Got 'Nux?�GNU/Linux and other free software support. It's GNU/Linux, not just Linux.

Sep 29th, 2006, 12:19 PM	#5
sarumont Hobbyist Programmer Join Date: Apr 2004 Location: /dev/urandom Posts: 154 Rep Power: 5	Check out 'man gethostbyname'. I believe that this library uses the standard DNS lookup stack in nix (typically in /etc/host.conf). __________________ "Time is an illusion. Lunchtime doubly so."* -the late, great Douglas Adams

Sep 29th, 2006, 6:50 PM	#6
a thing Unverified User Join Date: Aug 2005 Location: none Posts: 146 Rep Power: 0	Umm... this is the shell forum, not the C forum. __________________ Warning: My posts may change (dramatically) within the first 15 minutes they're posted. Got 'Nux?�GNU/Linux and other free software support. It's GNU/Linux, not just Linux.

Sep 28th, 2006, 3:27 PM	#2
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	Do you want to check the existence of any domain - nslookup? Options let you specify a domain to limit the search. You can also specify the DNS box. I'm not sure what you meant by a DNS domain in this context....

Oct 3rd, 2006, 10:38 PM	#10
a thing Unverified User Join Date: Aug 2005 Location: none Posts: 146 Rep Power: 0	Your proposed solution has given me a better idea. Ping gives the packet loss percent. All I need to do is check if that's like <=15. Damn I should learn awk. __________________ Warning: My posts may change (dramatically) within the first 15 minutes they're posted. Got 'Nux?�GNU/Linux and other free software support. It's GNU/Linux, not just Linux. Last edited by a thing; Oct 3rd, 2006 at 10:59 PM.

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