In this tutorial, you will learn-

What is a Computing Environment?

The Computing environment is the Platform(Platform = Operating System+ Processor) where a user can run programs.

What is a Variable?

In computer science, a variable is a location for storing a value which can be a filename, text, number or any other data. It is usually referred to with its Symbolic name which is given to it while creation. The value thus stored can be displayed, deleted, edited and re-saved.

Variables play an important role in computer programming because they enable programmers to write flexible programs. As they are related to the Operating system that we work on, it is important to know some of them and how we can influence them.

What are Environment variables?

Environment variables are dynamic values which affect the processes or programs on a computer. They exist in every operating system, but types may vary. Environment variables can be created, edited, saved, and deleted and give information about the system behavior.

Environment variables can change the way a software/programs behave.

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E.g. $LANG environment variable stores the value of the language that the user understands. This value is read by an application such that a Chinese user is shown a Mandarin interface while an American user is shown an English interface.

Let's study some common environment variables -

Variable

Description

PATH This variable contains a colon (:)-separated list of directories in which your system looks for executable files.
Linux - Environment Variables
When you enter a command on terminal, the shell looks for the command in different directories mentioned in the $PATH variable. If the command is found, it executes. Otherwise, it returns with an error 'command not found'.
USER The username
HOME Default path to the user's home directory
EDITOR Path to the program which edits the content of files
UID User's unique ID
TERM Default terminal emulator
SHELL Shell being used by the user

Accessing Variable values

In order to determine value of a variable, use the command

echo $VARIABLE

Variables are- Case Sensitive. Make sure that you type the variable name in the right letter case otherwise you may not get the desired results.

Linux - Environment Variables

The 'env' command displays all the environment variables.

Linux - Environment Variables

Set New Environment Variables

You can create your own user defined variable, with syntax

VARIABLE_NAME= variable_value

Again, bear in mind that variables are case-sensitive and usually they are created in upper case.

Linux - Environment Variables

Deleting Variables

The following syntax can be used to remove a Variable from the system.

unset variablename

Linux - Environment Variables

This would remove the Variable and its value permanently.

Summary:

  • Environment variables govern the behavior of programs in your Operating System.
Command Description
echo $VARIABLE To display value of a variable
env Displays all environment variables
VARIABLE_NAME= variable_value Create a new variable
unset   Remove a variable
export Variable=value To set value of an environment variable

 

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