how to extract just the IP address from a DNS query

Question

On Alpine Linux, I'd like to know how to extract just the IP address from a DNS / dig query. The query I'm running looks like this:

lab-1:/var/# dig +answer smtp.mydomain.net +short   
smtp.ggs.mydomain.net
10.11.11.11

I'd like to be able to get just the IP address returned. I'm currently playing around with the bash pipe and the awk command. But so far, nothing I've tried is working.

Thanks.

weird, it works for me on `centos`.. wonder what version of `dig` you are using? What distro(or os)? — man0v, Feb 26 '18 at 14:19

score 29 · Accepted Answer · answered Feb 26 '18 at 14:38

29

I believe dig +short outputs two lines for you because the domain you query, smtp.mydomain.net is a CNAME for smtp.ggs.mydomain.net, and dig prints the intermediate resolution step.

You can probably rely on the last line from dig's output being the IP you want, though, and therefore the following should do:

dig +short smtp.mydomain.net | tail -n1

answered Feb 26 '18 at 14:38

dhag

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What if it returns 2 IPs (2 A records)? – Matt White Nov 19 '21 at 21:29

score 8 · Answer 2 · answered Feb 26 '18 at 16:16

8

@dhag's answer sounds good; if you do not want to “rely on the last line from dig's output being the IP” you can use grep to extract just the numerical IP address:

dig +short smtp.mydomain.net | grep '^[.0-9]*$'

answered Feb 26 '18 at 16:16

Renardo

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@JordanBrough No, it doesn't – annahri May 31 '20 at 10:36

how to extract just the IP address from a DNS query

2 Answers2