Linux Environment Variables: Learn How to Read and Set on a Linux VPS

This knowledge base will walk you through the Linux environment variables in detail so you can quickly understand and alter simple commands on your virtual private server (VPS). Now let us get going!

What is Environment Variable?

Environment variables are dynamic values that have an immediate impact on the server’s processes or programs. They live on all operating systems and come in various varieties. These variables are simple to create, save, change, and remove.
Linux environment variables serve as stand-ins for any data that is kept on file within the system and includes information from programs that are run from shells or subshells.
An object with a name that holds data needed by one or more applications is called a variable. This indicates that it is a variable having a name and a value.

Variables – Variable is nothing but the data stored somewhere in the memory which is referenced by some indicator (variable name).
The value of Environment Variable can be the location of all executable files in the file system, the default editor that should be used, or it can be the system locale settings.
Thus, environment variables provide an easy way to share configuration settings between multiple applications and process in Linux.

Working of Environmental Variables :

Whenever you execute a shell session, in the backend, a process takes place to collect and compile information that should be available to the shell process and its child process. It is responsible to obtain the data from these settings from a variety of different files and settings on the system.
The environment is implemented in the form of a string that represents the key-value pairs. Multiple values are separated by semicolon (:) characters. The pair looks something like this :

KEY=value1:value2: .....

If the value contains white-space then the quotations are used :

KEY=”value with spaced”

The KEY in such examples are variables. They can be of type (a) Environmental variables or (b) Shell variables

Commands for Linux Environment Variable

Some common Linux environment variable commands that can help you to understand the Linux working will be discussed in this tutorial. Make a note that in order to modify any variables, you will need to access your VPS by using SSH.

1) How to View Linux Environment Variables?

Printenv allows you to view the entire list of environment variables on your Linux distribution.
You will get a large output by simply using it on your Ubuntu system.

To manage the output you can use piping in a modifier :

printenv | less

Every line in the command contains the name of the Linux environment variable that is followed by = and the value.
e.g.:

HOME=/home/jack

where :
Home is a Linux environment variable. This variable contains the value set as /home/Jack directory.

Environment variables are not case sensitive but still, are mostly used in upper case.
In this example, the output of printenv displays all environment variables in uppercase.

But, the important point to note here is that Linux environment variables are case sensitive.
If you wish to see the value of a specific environment variable, you can do it by passing the name of that variable as an argument to the printenv command. The string will look like this :

printenv HOME

Output :

/home/jack

The other method to display the value of an environment is by using the echo command like this :

echo $USER

Output :

Jack

Creating a New Linux Environment Variable

Syntax :

export VAR="value"

where,

• export: command used to create a variable
• VAR: the name of the variable
• =: it shows that the following section is the value
• “value” : the actual value

Command :

export jack ="hostvento"

2) To change the value of Timezone variable

Command to view the current output :

date

To edit the current time, use the export command :

export TZ=" US/Pacific"

Related: How to Change Timezone in Ubuntu?This way the variable value has been changed. To view the changes use date command, this gives you the output as per the changes made in the Linux environment variable.

3) To UNSET the Value of Linux Environment Variable

Syntax:

unset VAR

where,
• unset stands for the command itself
• VAR stands for the variable we want to unset

e.g: let’s unset the timezone variable using

unset TZ

This command will take the timezone to its default value which can be again checked by using date command.

The setting and unsetting of a Linux environmental variable via command line affects only the currently running sessions. In order to make your settings work continuously during the login sessions, you will have to defend the environment variables in your personal initialization file i.e. .bash_profile.

Local and Global Linux Environment Variable

Global variable :

In a computing program, Global variable is a construct and type of variable that is declared outside the function and thus, is accessible to all the functions throughout the program. A group of global variables are combined together to form the global environment that defines various aspects of a program or the environment when the program runs. A global variable is generally declared at the top of all functions, this is the reason that it can be used anywhere in the program.

Local variable :

A variable declared as local is given the local scope. That means it is visible only within the block of code in which it appears. In any function, a local variable has its meaning limited only within that function block.

Let’s take an example :
Global_var and local_var are the global and local variables respectively.

Var Global_val=60;

Function Fun()
{
var local_var = 30;
}

The global environment variables are visible from a shell session of any child processes that the shell spawns.
On the other hand, the local variable can be available in the shell only in which it is created.

For system environment variables, uppercase letters are used so as to differentiate them from normal environment variables.

Let’s see how you can set a Local Linux Environment Variable –

Note: in the below example, local_var is only visible in the current shell :

local_var=jack

echo $local_var

jack

To create global environment variable use the export command:

export Global_var=Hello

bash

echo $Global_var

The output will be:

Hello

From all the above examples you might have understood how you can set Environment variables to your VPS. To explore further here is a list of some commonly used variables in Linux that you can try by yourself.

System Variable	Meaning	To view Variable Value Type
HOSTNAME	The name of your system (computer).	echo $HOSTNAME
HISTFILE	It is a name of a file in which command history is saved.	echo $HISTFILE
HISTFILESIZE	The maximum number of lines contained in the history file.	echo $HISTFILESIZE
HISTSIZE	The total number of commands to remember in the command history. By default, its value is 500.	echo $HISTSIZE
CDPATH	The search path for the cd command.	echo $CDPATH
HOME	The home directory of the current user.	echo $HOME
BASH_VERSION	It holds the version of this instance of bash.	echo $BASH_VERSION
LANG	It is used to determine the locale category for any category not specifically select with a variable starting with LC_ .	echo $LANG
IFS	The Internal Field Separator that is used for word splitting after expansion and to split lines into words with the read builtin command. The default value is .	echo $IFS
PATH	The search path for commands. It is a colon-separated list of directories in which the shell looks for commands.	echo $PATH
PSl	Your prompt settings.	echo $PS1
TERM	Your login terminal type.	echo $TERM export TERM=vt100
SHELL	Set path to login shell.	echo $SHELL
DISPLAY	Set X display name.	echo $DISPLAY export DISPLAY=:0.1
EDITOR	Set name of default text editor.	export EDITOR=/usr/bin/vim
TMOUT	The default timeout for the read builtin command. Also in an interactive shell, the value is interpreted as the number of seconds to wait for input after issuing the command. If not input provided it will logout user.	echo $TMOUT

Conclusion –

Operating basic Linux Environment variables is very easy, isn’t it?
Just be careful and do some research before performing any modification and do brush up your skills regularly.
Did you find this tutorial helpful? Let us know in the comment section.