Export Command in Linux Explained
The export command in Linux is used for creating environment variables. Understand how it works and how you can use export command for practical usage.
The export command in Linux is used for creating environment variables. You can use it like this:
or a shorthand like this to assign it a value immediately:
You can see the value of exported variables with the echo command:
To make the changes permanent, you should add it to the ~/.bashrc file.
That was just the quick summary. Let’s see it in details to understand it better.
Understanding how export command works
In the example below, I declare a shell variable var and assign it a value 3. It’s a shell variable for now.
abhishek@nuc:~$ var=3 abhishek@nuc:~$ echo $var 3
If I exit the terminal and open a new terminal, this shell variable will disappear. If I want to use this variable in a shell script, it won’t work. Similarly, if I switch user (and thus initiating a new shell with this user), this shell variable won’t be available:
abhishek@nuc:~$ su prakash Password: prakash@nuc:/home/abhishek$ echo $var
Now, let’s go back to the previous user (and thus the previous shell where I declared the shell variable). You can see that the variable still exists here (because we didn’t terminate this shell session yet):
prakash@nuc:/home/abhishek$ exit exit abhishek@nuc:~$ echo $var 3
So, now if I use the export command on the variable
var here, it will become an environment variable and it will be available to all the subshells, users and shell scripts in this session.
abhishek@nuc:~$ export var abhishek@nuc:~$ echo $var 3 abhishek@nuc:~$ su prakash Password: prakash@nuc:/home/abhishek$ echo $var 3
You can check all the environment variables using the printenv command:
Make exported shell variables ‘permanent’ with bashrc file
But the struggle doesn’t end here. If you close the session, exit the terminal, log out or reboot your system, your environment variable will disappear again.
This is why it’s a common practice to add the export commands to the runtime configuration (rc) file of your shell.
Every shell has this rc file located in the user’s home directory which is used to determine variables and other configuration when the shell is started. As a user, you can use this rc file to customize your shell and its behavior.
If you are using bash shell, you should have a bashrc file at ~/.bashrc. You can either edit this file in a text editor like Vim or you can just append export var=3 (or whatever you are exporting) to this file.
Once done, you should use the source command to make the changes available immediately.
A good practice is to keep all the user defined environment variables at one place.
Why use export command?
One of the most common use of the export command is when you want to add something to the path so that your Linux system will find the certain command/executable file.
For example, if you installed maven and you want to be able to run it, you should add the directory location of maven executables to the path like this:
What does it do? It adds this directory location to the path. When you try to run a command in Linux, your system searches for its executable (usually in bin directory) in the directories mentioned in the PATH variable.
abhishek@nuc:~$ echo $PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin abhishek@nuc:~$ export PATH=/opt/maven/bin:$PATH abhishek@nuc:~$ echo $PATH /opt/maven/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
I highly recommend reading about Linux directory structure to have a better idea.
Bonus Tip: Remove a variable from exported list
Suppose you want to remove an ‘exported’ variable. You can use the negate option in this fashion:
export -n myvar
Keep in mind that this will not reset the value of the variable. It will just turn the exported global variable into a local variable. It will continue to have the same value you had set earlier.
If you want to remove the variable from the exported list as well as remove its assigned value, use the unset option:
I hope you have a better idea of the export command in Linux now. If you have doubts, please feel free to ask in the comment section.