How to set proxy for your terminal in linux

open the following file:

 /root/etc/apt/apt.conf   (if it is not there, then create it) 

and then write following into it:

Acquire::http::proxy "http://your_user_name:Your_password@ip_address_of proxy:8080/";
Acquire::ftp::proxy "ftp://your_user_name:Your_password@ip_address_of proxy:8080/";
Acquire::https::proxy "https://your_user_name:Your_password@ip_address_of proxy:8080/";