Environment variables in Ubuntu

The following is a exstract from Ubuntu help

The can be used to set enviroment variables in the terminal: ~/.bashrc

Session-wide environment variables

In
order to set environment variables in a way that effects a user's
entire desktop session, one may place commands to set their values in
one of the "hidden" script files in the user's home directory. The more
common such files are outlined below.

• ~/.profile
  – This is probably the best file for placing environment variable
  assignments in, since it gets executed automatically by the DisplayManager during the startup process desktop session as well as by the login shell when one logs-in from the textual console.

• ~/.bash_profile or ~./bash_login
  – If one of these file exist, bash executes it rather then "~/.profile"
  when it is started as a login shell. (Bash will prefer
  "~/.bash_profile" to "~/.bash_login"). However, these files won't
  influence a graphical session by default.

• ~/.bashrc
  – Because of the way Ubuntu currently sets up the various script files
  by default, this may be the easiest place to set variables in. The
  default configuration nearly guarantees that this file will be executed
  in each and every invocation of bash as well as while logging in to the
  graphical environment. However, performance-wise this may not be the
  best thing to do since it will cause values to be unnecessarily set
  many times.

System-wide environment variables

Environment
variable settings that effect the system as a whole (rather then just a
particular user's desktop session) can be placed in any of the many
system-level scripts that get executed when the system or the desktop
session are loaded. Ubuntu defines several locations dedicated to
placing such settings:

• /etc/profile
  – This file gets executed whenever a bash login shell is entered (e.g.
  when logging in from the console or over ssh), as well well as by the
  DisplayManager when the desktop session loads. This is
  probably the file you will get referred to when asking veteran UNIX
  system administrators about environment variables. In Ubuntu, however
  this file does little more then invoke the /etc/bash.bashrc file.

• /etc/bash.bashrc – This is is the system-wide version of the ~/.bashrc file. Ubuntu is configured by default to execute this file whenever a user enters a shell or the desktop environment.

• /etc/environment
  – This file is specifically meant for system-wide environment variable
  settings. It is not a script file, but rather consists of assignment
  expressions, one per line. Specifically, this file stores the
  system-wide locale and path settings.