The ifconfig command displays details of every active network interface available on the system. However, we can restrict it to a specific interface using the following command:

$ ifconfig iface_name 

Consider this example:

$ ifconfig wlan0 
wlan0     Link encap:EthernetHWaddr 00:1c:bf:87:25:d2 
inet addr:192.168.0.82 Bcast:192.168.3.255 Mask:255.255.252.0 
inet6 addr: fe80::3a2c:4aff:6e6e:17a9/64 Scope:Link 
UP BROADCAST RUNNINT MULTICAST  MTU:1500 Metric:1 
RX Packets... 

To control a device, we need the IP address, broadcast address, hardware address, and subnet mask:

•  HWaddr 00:1c:bf:87:25:d2: This is the hardware address (MAC address)
•  inet addr:192.168.0.82: This is the IP address
•  Bcast:192.168.3.255: This is the broadcast address
•  Mask:255.255.252.0: This is the subnet mask

To extract the IP address from the ifconfig output, use this command:

$ ifconfig wlan0 | egrep -o "inetaddr:[^ ]*" | grep -o "[0-9.]*" 
192.168.0.82 

The egrep -o "inetaddr:[^ ]*" command returns inet addr:192.168.0.82. The pattern starts with inetaddr: and ends with any non-space character sequence (specified by [^ ]*). The next command, grep -o "[0-9.]*" reduces its input to only numbers and periods, and prints out an IP4 address.