To allow global internet access through a proxy server you can add the code below to the file /etc/bash.bashrc.
export http_proxy=http://10.0.4.1:3128
To have immediate effect without need for a reboot type:
source /etc/bash.bashrc
For temporary http proxy just type
export http_proxy="http://10.0.0.0.:3128"
Tested with Debian distros