Read an Interface's IP Address

You need the IPv4 address bound to one interface. /root/net/task.txt names the interface (it differs per session), and a capture of ip addr show is saved at /root/net/ipaddr.txt. Read it and record THAT interface's IPv4 address (without the /prefix) to /root/answers/iface_ip.txt. The capture also lists loopback, other NICs and docker0.