Parse blocks in curly brackets

Question

I'm trying to parse a dhcpd.conf file that looks like this:

authoritative;

subnet x.x.x.x netmask x.x.x.x {
    range x.x.x.x x.x.x.x;
    deny unknown-clients;
    default-lease-time 86400;
    max-lease-time 86400;
    option domain-name "bla";
    option domain-name-servers x.x.x.x;
    option broadcast-address x.x.x.x;
    option subnet-mask x.x.x.x;
    option routers x.x.x.x;

    host host1 {
            hardware ethernet 00:e1:4c:68:00:53;
            fixed-address 1.1.1.1;
    }

    host host2 {
            hardware ethernet 01:e2:4d:69:01:54;
            fixed-address 2.2.2.2;
    }

    host host3 {
            hardware ethernet 02:e3:4e:70:02:55;
            fixed-address 3.3.3.3;
    }

    host host4 {
            hardware ethernet 03:e4:4f:71:03:56;
            fixed-address 4.4.4.4;
    }

    host host5 {
            hardware ethernet 04:e5:5f:72:04:57;
            fixed-address 5.5.5.5;
    }
}

In the end I need to loop though the host blocks (no matter their name) and assign the MAC address and IP address to variables in order to process the combination. So far I managed to do this with only one variable:

for MAC in `cat /etc/dhcp/dhcpd.conf | grep "hardware ethernet" | awk '{ print $3 }' | tr ";" " "`
do
    echo "Found MAC address: " $MAC "Found IP: <I need the IP Variable here...>" 
done

Maybe it's better to somehow "grep" the host blocks in order to loop through these, but I don't know how to do this.

Could anybody give me a hint on how to do this?

Thanks

Answer 1

Given that the input file is in the exact format (MAC followed by IP), following sed one liner will give a list of "MAC,IP" csv pairs. You can parse it and do what ever you want.

sed -n '/\s*hardware ethernet/{s/\s*hardware ethernet \(.*\);/\1/;N;s/\([a-z0-9:]*\)\s*fixed-address \(.*\);/\1,\2/p}' /etc/dhcp/dhcpd.conf

Output:

00:e1:4c:68:00:53,1.1.1.1
01:e2:4d:69:01:54,2.2.2.2
02:e3:4e:70:02:55,3.3.3.3
03:e4:4f:71:03:56,4.4.4.4
04:e5:5f:72:04:57,5.5.5.5

To produce the exact output as in your example,

sed -n '/\s*hardware ethernet/{s/\s*hardware ethernet \(.*\);/\1/;N;s/\([a-z0-9:]*\)\s*fixed-address \(.*\);/Found MAC address: \1, Found IP: \2/p}' /etc/dhcp/dhcpd.conf

Output:

Found MAC address: 00:e1:4c:68:00:53, Found IP: 1.1.1.1
Found MAC address: 01:e2:4d:69:01:54, Found IP: 2.2.2.2
Found MAC address: 02:e3:4e:70:02:55, Found IP: 3.3.3.3
Found MAC address: 03:e4:4f:71:03:56, Found IP: 4.4.4.4
Found MAC address: 04:e5:5f:72:04:57, Found IP: 5.5.5.5

---

EDIT

You can extract MAC and IP from each pair and do something with them as follows.

for v in $(sed -n '/\s*hardware ethernet/{s/\s*hardware ethernet \(.*\);/\1/;N;s/\([a-z0-9:]*\)\s*fixed-address \(.*\);/\1,\2/p}' /etc/dhcp/dhcpd.conf); do
    mac="${v%,*}"
    ip="${v#*,}"
    echo "MAC: $mac"
    echo "IP: $ip"
done