How to Set and List Environment Variables on Linux

Introduction

Before we begin talking about how to set and list environment variables on Linux, let's briefly understand – What is an Environment Variable?

An environment variable stores values for software and OS. It provides essential information about the system's configuration, such as the location of important files or paths to directories.

Environment variables are commonly used to customize the behavior of software and enable seamless interaction between different programs. By defining these variables, developers can ensure that their applications run correctly across various systems. Understanding environment variables is crucial for software development and system administration.

In this tutorial, you will set and list environment variables on Linux. We will also address a few FAQs on how to set and list environment variables on Linux.

Advantages of Environment Variable

1. Flexibility: Environment variables adapt software behavior across systems without code changes.
2. Customization: Variables allow users to configure software to their specific needs.
3. Security: Sensitive data, like API keys, can be securely stored and accessed through environment variables.
4. Modularity: Variables enable modular code and easier integration of different software components.
5. Portability: Programs become portable when using environment variables, working consistently across various environments.

Environment Variables and Shell Variables

The following is the format for variables:

KEY=value
KEY="Some other value"
KEY=value1:value2

• The variables' names are case-sensitive. Environment variables should be named in UPPER CASE by convention.
• When assigning several values to the variable, the colon : character must be used to separate them.
• The equals = sign has no space surrounding it.

Environment variables and shell variables are the two basic groups of variables.

Environment variables are system-wide variables that are passed down to all spawned child processes and shells.

Variables that only pertain to the current shell instance are known as shell variables. Internal shell variables are unique to each shell, such as zsh and bash.

On Linux, there are numerous commands that may be used to list and set environment variables:

• env - This command allows you to run a different program in a different environment without having to change the current one. It prints a list of the current environment variables when used without an argument.
• printenv - This command displays all or a subset of the environment variables.
• set - This command changes the state of shell variables. It prints a list of all variables, including environment and shell variables, as well as shell functions, when used without an argument.
• unset - This command removes the shell and environment variables from the command line.
• export - This command is used to change the environment variables.

List Environment Variables

Printenv is the most commonly used command for displaying environment variables. Only the value of the variable is displayed if the name of the variable is supplied as an argument to the command. Printenv prints a list of all environment variables, one variable per line, if no argument is given.

To see the value of the HOME environment variable, for example, type:

printenv HOME

The path of the currently logged in user will be printed in the output:

Output

/home/vegastack

You may also use the printenv command with many arguments:

printenv LANG PWD

Output

en_US
/home/VegaStack

The printenv or env command will provide a list of all environment variables if called without any arguments:

printenv

You will get an output like below:

Output

LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35;...
LESSCLOSE=/usr/bin/lesspipe %s %s
LANG=en_US
S_COLORS=auto
XDG_SESSION_ID=5
USER=linuxize
PWD=/home/linuxize
HOME=/home/linuxize
SSH_CLIENT=192.168.121.1 34422 22
XDG_DATA_DIRS=/usr/local/share:/usr/share:/var/lib/snapd/desktop
SSH_TTY=/dev/pts/0
MAIL=/var/mail/linuxize
TERM=xterm-256color
SHELL=/bin/bash
SHLVL=1
LANGUAGE=en_US:
LOGNAME=linuxize
XDG_RUNTIME_DIR=/run/user/1000
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
LESSOPEN=| /usr/bin/lesspipe %s
_=/usr/bin/printenv

Some of the most prevalent environmental variables are listed below:

• USER - The user who is currently logged in.
• HOME - The current user's home directory.
• EDITOR - To be used as the default file editor. When you type edit in your terminal, this is the editor that will be used.
• SHELL - The current user's shell path, for example, bash or zsh.
• LOGNAME - The current user's name is displayed here.
• PATH - When running commands, this is a list of directories that will be searched. When you run a command, the system will look through those folders in this order and utilize the first executable that it finds.
• LANG - The current settings for the locale.
• TERM - The current terminal emulation.
• MAIL - The current user's mail is saved at this location.

Only the environment variables are printed by the printenv and env commands. The set command can be used to retrieve a list of all variables, including environment, shell and variables, and shell functions:

set

Output

BASH=/bin/bash
BASHOPTS=checkwinsize:cmdhist:complete_fullquote:expand_aliases:extglob:extquote:force_fignore:histappend:interactive_comments:login_shell:progcomp:promptvars:sourcepath
BASH_ALIASES=()
BASH_ARGC=()
BASH_ARGV=()

You'll probably want to pipe the output to the less command because the command will display a long list of all variables.

set | less

The echo command can also be used to print a shell variable. To print the value of the BASH_VERSION variable, for example, type:

echo $BASH_VERSION

Output

4.4.19(1)-release

Setting Environment Variables

We'll start with Shell Variables and then move on to Environment Variables to further show the differences between the two.

To create a new shell variable with the name MY_VAR and the value VegaStack, simply type:

MY_VAR='VegaStack'

You can check if the variable is set by echo $MY_VAR or filtering the set command output with grep set | grep MY VAR:

echo $MY_VAR

Output

VegaStack

To see if this variable is an environment variable, use the printenv command:

printenv MY_VAR

The variable's output will be empty, indicating that it is not an environment variable.

Attempting to print the variable in a new shell will result in empty output.

bash -c 'echo $MY_VAR'

Environment variables are set using the export command.

Simply export the shell variable as an environment variable to generate an environment variable:

export MY_VAR

Run the following command to see if this is true:

printenv MY_VAR

Output

VegaStack

If you try to print the variable again in a fresh shell, the variable name will appear on your terminal:

bash -c 'echo $MY_VAR'

Output

VegaStack

You can also use a single line to set environment variables:

export MY_NEW_VAR="My New Var"

Environment Variables created in this way create variables that are only available in the current session. All variables will be lost if you open a new shell or log out.

Persistent Environment Variables

Environment variables must be defined in the bash configuration files if they are to be persistent. When you start a new session in most Linux versions, environment variables are read from the following files:

• /etc/environment - Set up system-wide environment variables with this file. Variables in this file are formatted as follows:

FOO=bar
VAR_TEST="Test Var"

• /etc/profile - When a bash login shell is entered, variables set in this file are loaded. You must use the export command to declare environment variables in this file:

export JAVA_HOME="/path/to/java/home"
export PATH=$PATH:$JAVA_HOME/bin

Shell configuration files are customized to each user. If you're using Bash, for example, you can declare variables in the ~/.bashrc:

export PATH="$HOME/bin:$PATH"

Use the source command to load the new environment variables into the current shell session:

source ~/.bashrc

FAQs to Set and List Environment Variables on Linux

Conclusion

We've taught you how to set and list environment and shell variables in this tutorial.

If you have any queries, please leave a comment below and we’ll be happy to respond to them.