How to use apt-get / aptitude behind proxy server

if you get internet connection via a proxy server, you might be able you web browser but unable to use apt-get, aptitude or any other APT gui.
To over come this problem,

1. Edit your /etc/bash.bashrc file as root

• If you use Kubuntu
  

sudo kate /etc/bash.bashrc

• If you use Ubuntu

sudo kate /etc/bash.bashrc

2. Append following two line into your file and save it

export http_proxy=http://user:password@my.proxy.server:port/
export ftp_proxy=http://user:password@my.proxy.server:port/

• N.B. Replace "user" with your username "password" with your password, "my.proxy.server" with your proxy server address and "port" with your port.
• If your proxy server doesn't require authentication simply use server address and port
• Mine is

export http_proxy=http://192.248.16.90:3128/
export ftp_proxy=http://192.248.16.90:3128/

• Then on console type

source ~/.bashrc

• to effect the changes

Reference 1:
Reference 2: