to assign static ip manually using terminal or shell.first you need killall dhclient.

run below command

$killall dhclient

then run below step (here i am using my network example)

$ifconfig eth0 up 192.168.1.5 netmask 255.255.255.0

above step is used for assigning the ip

now you need to add default gateway,first you need check your gateway by running below command

$route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

now ping before adding default gateway

$ping 192.168.1.1
PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=2.34 ms

now add the default gateway using below command

$route add default gw 192.168.1.1

now your done with assigning static ip manually