How to Set and List Environment Variables in Linux
In Linux and Unix based systems environment variables are a set of dynamic named values, stored within the system that are used by applications launched in shells or subshells. In simple words, an environment variable is a variable with a name and an associated value.
Environment variables allow you to customize how the system works and the behavior of the applications on the system. For example, the environment variable can store information about the default text editor or browser, the path to executable files, or the system locale and keyboard layout settings.
In this guide, we will explain to read and set environment and shell variables.
Environment Variables and Shell Variables #
Variables have the following format:
KEY=value KEY="Some other value" KEY=value1:value2 - The names of the variables are case-sensitive. By convention, environment variables should have UPPER CASE names.
- When assigning multiple values to the variable they must be separated by the colon : character.
- There is no space around the equals = symbol.
Variables can be classified into two main categories, environment variables, and shell variables.
Environment variables are variables that are available system-wide and are inherited by all spawned child processes and shells.
Shell variables are variables that apply only to the current shell instance. Each shell such as zsh and bash , has its own set of internal shell variables.
There are several commands available that allow you to list and set environment variables in Linux:
- env – The command allows you to run another program in a custom environment without modifying the current one. When used without an argument it will print a list of the current environment variables.
- printenv – The command prints all or the specified environment variables.
- set – The command sets or unsets shell variables. When used without an argument it will print a list of all variables including environment and shell variables, and shell functions.
- unset – The command deletes shell and environment variables.
- export – The command sets environment variables.
List Environment Variables #
The most used command to displays the environment variables is printenv . If the name of the variable is passed as an argument to the command, only the value of that variable is displayed. If no argument is specified, printenv prints a list of all environment variables, one variable per line.
For example, to display the value of the HOME environment variable you would run:
The output will print the path of the currently logged in user:
You can also pass more than one arguments to the printenv command:
If you run the printenv or env command without any arguments it will show a list of all environment variables:
The output will look something like this:
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 Below are some of the most common environment variables:
- USER — The current logged in user.
- HOME — The home directory of the current user.
- EDITOR — The default file editor to be used. This is the editor that will be used when you type edit in your terminal.
- SHELL — The path of the current user’s shell, such as bash or zsh.
- LOGNAME — The name of the current user.
- PATH — A list of directories to be searched when executing commands. When you run a command the system will search those directories in this order and use the first found executable.
- LANG — The current locales settings.
- TERM — The current terminal emulation.
- MAIL — Location of where the current user’s mail is stored.
The printenv and env commands print only the environment variables. If you want to get a list of all variables, including environment, shell and variables, and shell functions you can use the set command:
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=() The command will display a large list of all variables so you probably want to pipe the output to the less command.
You can also use the echo command to print a shell variable. For example, to print the value of the BASH_VERSION variable you would run:
Setting Environment Variables #
To better illustrate the difference between the Shell and Environment variables we’ll start with setting Shell Variables and then move on to the Environment variables.
To create a new shell variable with the name MY_VAR and value Linuxize simply type:
You can verify that the variable is set by using either echo $MY_VAR of filtering the output of the set command with grep set | grep MY_VAR :
Use the printenv command to check whether this variable is an environment variable or not:
The output will be empty which tell us that the variable is not an environment variable.
You can also try to print the variable in a new shell and you will get an empty output.
The export command is used to set Environment variables.
To create an environment variable simply export the shell variable as an environment variable:
You can check this by running:
If you try to print the variable in a new shell this time you will get the variable name printed on your terminal:
You can also set environment variables in a single line:
export MY_NEW_VAR="My New Var"Environment Variables created in this way are available only in the current session. If you open a new shell or if you log out all variables will be lost.
Persistent Environment Variables #
To make Environment variables persistent you need to define those variables in the bash configuration files. In most Linux distributions when you start a new session, environment variables are read from the following files:
- /etc/environment — Use this file to set up system-wide environment variables. Variables in this file are set in the following format:
export JAVA_HOME="/path/to/java/home"export PATH=$PATH:$JAVA_HOME/bin
To load the new environment variables into the current shell session use the source command:
Conclusion #
In this guide, we have shown you how to set and list environment and shell variables.
Feel free to leave a comment if you have any questions.
What are my environment variables? [closed]
Wow that was fast! I guess all the command do the trick. The export command gave me a lot of «declare -x» in front. Thanks guys!
It was inappropriate to close this question as off topic. When programming on Linux, as I am doing at the moment, it is often useful to discover what the environmental variables are. Quite a lot of people have found this to be a useful question, including me.
4 Answers 4
I am not sure if thats what you want, but try printenv
This will show you all your environment variables.
Just execute env in a terminal.
$ env TERM=xterm SHELL=/bin/bash USER=joksnet USERNAME=joksnet DESKTOP_SESSION=gnome PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games PWD=/home/joksnet GDM_KEYBOARD_LAYOUT=us LANG=en_US.utf8 HOME=/home/joksnet DISPLAY=:0.0 COLORTERM=gnome-terminal _=/usr/bin/env Type export without any parameters.
SET(P) POSIX Programmer’s Manual SET(P) NAME set - set or unset options and positional parameters SYNOPSIS set [-abCefmnuvx][-h][-o option][argument. ] set [+abCefmnuvx][+h][+o option][argument. ] set -- [argument. ] set -o set +o DESCRIPTION If no options or arguments are specified, set shall write the names and values of all shell variables in the collation sequence of the current locale. Each name shall start on a separate line, using the format: "%s=%s\n", , The value string shall be written with appropriate quoting; see the description of shell quoting in Quoting . The output shall be suitable for reinput to the shell, setting or resetting, as far as possible, the variables that are currently set; read-only variables cannot be reset. env or printenv are better. In bash, set will also print all your defined functions, which on a system like ubuntu, is a very long printout.