How do I add environment variables?

I'm running Ubuntu 11.04. I use the terminal to start a bash session, and I want to add an environment variable:

$r@hajt:~$ env THEVAR=/example

But it's not working. It shows all the variables with THEVAR being the last one, but another call to env does not show THEVAR anymore- env | grep THEVAR returns nothing.

Similarly, scripts with export (export THEVAR=/example) or other variable assignments (THEVAR=/example) don't add the environment variable.

I know I'm doing something wrong, I know it should be something simple, but I just can't find what.

UPDATE: The real meaning of my question was this one:

• Can a shell script set environment variables of the calling shell?

(Anyway I'll choose the most voted answer and leave the edited title -that wasn't what I was asking)

env runs a program in a modified environment, then dismisses all the changes.

To set variable only for current shell:

VARNAME="my value"

To set it for current shell and all processes started from current shell:

export VARNAME="my value"      # shorter, less portable version

To set it permanently for all future bash sessions add such line to your .bashrc file in your $HOME directory.

To set it permanently, and system wide (all users, all processes) add set variable in /etc/environment:

sudo -H gedit /etc/environment

This file only accepts variable assignments like:

VARNAME="my value"

Do not use the export keyword here.

You need to logout from current user and login again so environment variables changes take place.

To set an environment variable once, use the export command in the prompt, not in a shell script:

$ export THEVAR=/example

The variable will be set for the rest of the shell session or until unset.

To set an environment variable everytime, use the export command in the .bashrc file (or the appropriate initialization file for your shell).

To set an environment variable from a script, use the export command in the script, and then source the script. If you execute the script it will not work.

For an explanation of the difference between sourcing and executing see this answer:

• What is the difference between executing a Bash script vs sourcing it?

To permanently add a new environment variable in Ubuntu (tested only in 14.04), use the following steps:

1. Open a terminal (by pressing CtrlAltT)
2. sudo -H gedit /etc/environment
3. Type your password
4. Edit the text file just opened:
   e.g. if you want to add FOO=bar, then just write FOO=bar in a new line
5. Save it
6. Once saved, logout and login again.
7. Your required changes are made.

To get the environment/var changes to persist after the script has completed, you have to usesource ./script.sh or the shorthand notation for source, ".", like . ./script.sh

Source will execute the commands in the script as if you have typed them in... so it does change some aspects of the script, such as exiting... so if your script checks something and decides to exit if false, for instance, via calling exit 0, it will terminate your current terminal / shell session.