What Are Environment Variables in Linux?

Environment Variables in Linux are dynamic values that the operating system and various applications use to determine information about the user environment. They are essentially variables that can influence the behavior and configuration of processes and programs on a Linux system. These variables are used to pass configuration information to programs and scripts, allowing for flexible and dynamic system management.

These variables, often referred to as global variables, play a crucial role in tailoring the system’s functionality and managing the startup behavior of various applications across the system. On the other hand, local variables are restricted and accessible from within the shell in which they’re created and initialized.

Linux environment variables have a key-value pair structure, separated by an equal (=) sign. Note that the names of the variables are case-sensitive and should be in uppercase for instant identification.

Key Features of Environment Variables

• Dynamic Values: They can change from session to session and even during the execution of programs.
• System-Wide or User-Specific: Some variables are set globally and affect all users and processes, while others are specific to individual users.
• Inheritance: Environment variables can be inherited by child processes from the parent process, making them useful for configuring complex applications.

Common Environment Variables

Here are some commonly used environment variables in Linux:

• HOME: Indicates the current user’s home directory.
• PATH: Specifies the directories where the system looks for executable files.
• USER: Contains the name of the current user.
• SHELL: Defines the path to the current user’s shell.
• LANG: Sets the system language and locale settings.

Setting and Using Environment Variables

Temporary Environment Variables in Linux

You can set environment variables temporarily in a terminal session using the export command: This command sets an environment variable named MY_VAR to true for the current session. Environment variables are used to store information about the environment in which programs run.

export MY_VAR=true
echo $MY_VAR

Example 1: Setting Single Environment Variable

For example, the following command will set the Java home environment directory.

Note that you won’t get any response about the success or failure of the command. As a result, if you want to verify that the variable has been properly set, use the echo command.

The echo command will display the value if the variable has been appropriately set. If the variable has no set value, you might not see anything on the screen.

OUTPUT :

Example 2: Setting Multiple Environment Variables

You can specify multiple values for a multiple variable by separating them with space like this:

<NAME>=<VALUE1> <VALUE2><VALUE3>

Example 3: Setting Multiple value for single Environment Variable

You can specify multiple values for a single variable by separating them with colons like this: <NAME>=<VALUE1>:<VALUE2>:<VALUE3>

The PATH variable contains a list of directories where the system looks for executable files. Multiple directories are separated by colons.

Permanent Environment Variables in Linux

To make MY_VAR available system-wide, follow these steps:

This command appends the line MY_VAR=”True” to the /etc/environment file, which is a system-wide configuration file for environment variables.

By adding this line, you make the MY_VAR variable available to all users and sessions on the system.

The use of sudo ensures that the command has the necessary permissions to modify /etc/environment

Example 1: Setting Single Environment Variable for all USERS

Breakdown of the Command

echo ‘MY_VAR=”true”‘: This command outputs the string MY_VAR=”true”. Essentially, echo is used to display a line of text.

| (Pipe): The pipe symbol | takes the output from the echo command and passes it as input to the next command. In this case, it passes the string MY_VAR=”true” to sudo tee.

sudo tee /etc/environment -a: sudo: This command is used to run commands with superuser (root) privileges. Since modifying /etc/environment requires administrative rights, sudo is necessary.

tee: The tee command reads from the standard input (which is the output of the echo command in this case) and writes it to both the standard output (displaying it on the terminal) and a file.

/etc/environment: This is the file where tee will write the output. The /etc/environment file is a system-wide configuration file for environment variables.

-a: The -a (append) option tells tee to append the input to the file rather than overwriting its contents. This ensures that any existing settings in /etc/environment are preserved and the new line is simply added to the end of the file.

This command is used to add a new environment variable (MY_VAR) to the system-wide environment variables file (/etc/environment). By appending it, you ensure that the new variable is available to all users and sessions across the entire system.

Example 2: Setting Multiple value for single Environment Variable for all USERS

You can specify multiple values for a single variable by separating them with colons like this: <NAME>=<VALUE1>:<VALUE2>:<VALUE3>

OUTPUT :

 

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