There are different versions of host so that might be the explanation. The idea is workable, though; get the verbose (debugging) output and parse out the fields you want. But in any case, to get the name and IP address of the name servers, you will need multiple queries -- one to get the names of the name servers, and another to look up their IP addresses. (Some sites put raw IP addresses in the NS records but this is strongly discouraged.)
I think Ikon misunderstood your question, perhaps because the output format you are suggesting is somewhat misleading (perhaps it should mention that these are the IP addresses of the name servers). The pipeline could be simplified a bit but the request of A records instead of NS records is wrong anyway.
I think you're getting the wrong result somehow; at least for me, b.iana-servers.net is 193.0.0.236 -- you're querying for $dom which is wrong, you should be querying for $server, but there can be other complications, too.
dig and host are not part of coreutils; on Ubuntu, at least, they're in the dnsutils and host packages, respectively, and there's also a separate bind9-host package which I believe contains a different version of host (hence, different output formats; originally host was also part of the dnsutils package, but many people wanted the Bind version, so they split it out).
example.com has two name servers. Their names are b.iana-servers.net and a.iana-servers.net. These are the servers which will tell you the IP address of example.com, should you ever ask for it. The way I understood your question, the IP addresses of the name servers is what you want your script to print.
Or, given the input unix.com, it should look up the name servers for unix.com (ns1.sitesolutions.com through ns4.sitesolutions.com) and print their IP addresses.
Did I not understand you correctly? If so, can you rephrase your question?
So you don't care at all about what the nameservers are? Or you want to query all the authoritative name servers in turn? In the former case, host -t a example.com is all you need. In the latter case, what you have (sort of) makes sense, except your version of the script fails to specify which name server to use (but obviously you know how to use dig @server to do that, or you can use host example.comb.iana-servers.net to specify b.i-s.n as the name server to use; but dig is certainly more scripter-friendly).
#!/bin/sh
host=$1
dig +short ns $host |
while read nameserver; do
dig +short @$nameserver $host | sed "s/^/IP for $host at $nameserver is /"
done
It's not a one-liner unless your lines have fractal dimensions but I hope that wasn't strictly a requirement.
It even works on my Ubuntu 8.04 platform. I'm in heaven.
I am struggling with echo'ing "IP for scallyroottest.com is" +"at"
from this command:
host -t ns example.com | while read dom ns server; do dig +short $dom; done but managed this poor example of a coding attempt using the example:
host -t ns example.com | while read dom ns server ; do echo "IP for" $dom "is" "<IP>" "at"; done
but it's still missing the do dig routine.
Not sure if/how it can be done. Can you have >1 do ; done routine?
Short of any clear answers, I am on my way to some serious homework.
You can have as many commands as you like between the "do" and "done", and of course, they can be new loops with "do" and "done" in them. Not sure where you'd need that, though. You can simply modify the sed script to shuffle things around in a different order if that's how you like them.
sed "s/.*/IP for $host is & at $nameserver"
The "s/from/to/" command in sed will substitute the stuff in "from" with the stuff in "to" on each line. In this case we are replacing the IP address printed by dig with the longer string. & retrieves the "from" string into the "to" string. Dot star is the regular expression for "everything on this line" (dot means any character, star means any number of times).
Just to show an alternate way of doing it, here's a loop which prints the message piecemeal.
#!/bin/sh
host=$1
dig +short ns $host |
while read nameserver; do
echo -n "IP for $host is "
dig +short @$nameserver $host | tr '\n' ' ' # replace final newline with space
echo "at $nameserver"
done
Or you can interpolate with backticks
echo IP for $host is `dig +short @$nameserver $host` at $nameserver
Backticks AKA grave accents (ASCII 96) capture the output of one command so you can use it in the command line of another command. Notice that those are not regular single quotes. Copy/paste them if you can't find them on your keyboard.
