One of my favorite things about grabbing things with scripts is just how many ways (and sometimes how needfully or needlessly convoluted you can make them) to grab the same pieces of information. For example, something as simple as what hosts you use to resolve names on a Mac. There are a number of ways to grab what DNS server a device is using in macOS. So when you’re running a script you might choose to grab DNS information one way or another, according to what you’re after. Some of this might seem more complicated than it should be. And that’s correct…
resolv.conf
The /etc/resolv.conf file is updated automatically to look at what servers are used to resolve names used for DNS. The easiest way to see theses to simply cat it and grep for nameserver:
cat /etc/resolv.conf | grep nameserver
scutil
The next way we’ll grab DNS information is using scutil. Here, we use the –dns option, which outputs a lot of DNS stuffs, including all the built-in resolvers:
scutil --dns
To just grab the name servers:
scutil --dns | grep nameserver
We can also simplify the output to just the servers with awk:
scutil --dns | grep nameserver | awk '{print$3}'
networksetup
The second way is using networksetup. This command has an option to get a DNS server in (shocker) -getdnsservers. However, you have to list the interface for each. So below we’ll dump all interfaces into an array using -listallhardwareports and then read them in using a for loop and querying the name servers.
interfaces=( "$(networksetup -listallhardwareports | grep Hardware | cut -c 16-900)" )
for i in "${interfaces[@]}"
do
networksetup -getdnsservers $i
done
The one tricky thing in this one is I initially forgot to quote the interfaces as they went into the array, which meant each word of the interface was an item in the array and therefore the -getdnsservers option failed. Once I quoted, it was all happy. The other thing I can point out is I used cut instead of sed because it was easier to quote; however, it seems unlikely the name can be more than 890 characters, so I think it’s fine…
dig
You can also use dig. Here, you’ll query for a name without using an @ option, but omit everything but the line with the server that responded:
dig google.com | grep SERVER:
The output is kinda’ fug:
;; SERVER: 4.2.2.2#53(4.2.2.2)
For simpler output, we’ll use sed to constrain the output to just what’s between the parenthesis:
dig google.com | grep SERVER: | sed 's/^.*(//;s/)$//'
nslookup
nslookup is a tool similar to dig, used for querying names. We’ll basically do the same thing as above, just using awk as it’s just a standard position in a line:
nslookup google.com | grep Server: | awk '{print$2}'
system_profiler
Then there’s system_profiler, the command line interface for System Profiler. Here, we can query the SPNetworkDataType. This is going to produce a lot of output, so we can limit it to just the DNS servers using grep to constrain to just the lines we want and awk for just the columns in those lines, as follows:
system_profiler SPNetworkDataType | grep "Domain Name Servers:" | awk '{print$4}'
hosts
@knapjack added to use hosts. I had to use verbose mode to pull the local name server as follows:
host -v -t ns google.com | grep Received | awk '{print $5}'
ipconfig
Thanks to the lovely Allister (@sacrilicious), we also have ipconfig to add to the list:
/usr/sbin/ipconfig getpacket en0 2> /dev/null | grep name_ | cut -d' ' -f3-
There are tons of ways to find things in macOS. Do you have a way to find a DNS server that I didn’t think of here?