network ip calculation with ifconfig

Most *nix are different. I’ll start with a plain Linux output

ifconfig eth0
eth0: flags=4163  mtu 1500
        inet 93.184.216.34  netmask 255.255.255.0  broadcast 93.184.216.255

to get the network ip, I just bitwise-and the inet and the netmask. To do it with the shell, I convert the ip to an integer and use the & (AND) operator

IP=$(ifconfig eth0|grep inet|awk '{print $2}')
NM=$(ifconfig eth0|grep inet|awk '{print $4}')

I get my IP=93.184.216.34 and NM=255.255.255.0 out of the ifconfig output

IPDEC=0;IFS=. ;for f in $IP;do ((IPDEC*=256));((IPDEC+=$f));done
NMDEC=0;IFS=. ;for f in $NM;do ((NMDEC*=256));((NMDEC+=$f));done

By converting the IP-base-256 address, I get IPDEC=1572395042 and NMDEC=4294967040 in decimal

NWDEC=$((IPDEC&NMDEC))

That’s simple. My network IP is 1572395008

Let’s print it

NW=$((NWDEC/256/256/256)).$((NWDEC/256/256%256)).$((NWDEC/256%256)).$((NWDEC%256))
NW=93.184.216.0

Thanks for reading me that far. Ok let blogger Mathieu Trudel-Lapierre tell you : If you’re still using ifconfig, you’re living in the past

ip addr

ip shows your ip, and ipcalc do the calculation

ipcalc -n "$(ip -o -4  -br address show eth0 |awk '{print $3}')"
NETWORK=93.184.216.0