How to set temporary Linux env vars

Introduction

In the Linux operating system, environment variables play a crucial role in defining the working environment for applications and user sessions. These variables act as a communication channel between the system and the programs running on it, providing essential information and configuration settings. Understanding the concept of environment variables is fundamental for Linux users and developers, as they are extensively used to customize the system, manage application behavior, and automate various tasks.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL linux(("`Linux`")) -.-> linux/BasicSystemCommandsGroup(["`Basic System Commands`"]) linux(("`Linux`")) -.-> linux/UserandGroupManagementGroup(["`User and Group Management`"]) linux/BasicSystemCommandsGroup -.-> linux/declare("`Variable Declaring`") linux/BasicSystemCommandsGroup -.-> linux/source("`Script Executing`") linux/UserandGroupManagementGroup -.-> linux/env("`Environment Managing`") linux/UserandGroupManagementGroup -.-> linux/set("`Shell Setting`") linux/UserandGroupManagementGroup -.-> linux/export("`Variable Exporting`") linux/UserandGroupManagementGroup -.-> linux/unset("`Variable Unsetting`") subgraph Lab Skills linux/declare -.-> lab-419018{{"`How to set temporary Linux env vars`"}} linux/source -.-> lab-419018{{"`How to set temporary Linux env vars`"}} linux/env -.-> lab-419018{{"`How to set temporary Linux env vars`"}} linux/set -.-> lab-419018{{"`How to set temporary Linux env vars`"}} linux/export -.-> lab-419018{{"`How to set temporary Linux env vars`"}} linux/unset -.-> lab-419018{{"`How to set temporary Linux env vars`"}} end

Understanding Environment Variables in Linux

Understanding the concept of environment variables is fundamental for Linux users and developers, as they are extensively used to customize the system, manage application behavior, and automate various tasks.

What are Environment Variables?

Importance of Environment Variables

Environment variables are important for several reasons:

System Configuration: Environment variables are used to store system-wide configuration settings, such as the default shell, the system's language and locale, and the paths to important directories.
Application Behavior: Applications can use environment variables to determine their behavior, such as the default file paths, database connection details, and other runtime settings.
User Customization: Users can set their own environment variables to customize their working environment, such as setting the default editor, terminal preferences, or other personal settings.
Automation and Scripting: Environment variables are extensively used in shell scripts and automation tools to make the code more portable, configurable, and maintainable.

Accessing and Modifying Environment Variables

In Linux, you can access and modify environment variables using various commands and techniques:

## Displaying all environment variables
env
export
printenv

## Accessing the value of a specific variable
echo $VARIABLE_NAME

## Setting a new environment variable
export VARIABLE_NAME="value"

## Removing an environment variable
unset VARIABLE_NAME

Here's an example of setting and using an environment variable:

## Set a custom environment variable
export MY_APP_CONFIG="/path/to/config.ini"

## Use the variable in a script or application
my_app --config $MY_APP_CONFIG

By understanding the concept of environment variables and how to work with them, you can effectively manage your Linux system, customize your working environment, and build more robust and adaptable applications.

Defining and Managing Environment Variables

Environment variables in Linux can be defined and managed in various ways, depending on the scope and purpose of the variable. Understanding the different methods and best practices for defining and managing environment variables is crucial for effective system administration and application development.

Defining Environment Variables

Environment variables can be defined in several ways:

Temporary Environment Variables: These variables are only available within the current shell session and are not persisted across reboots or new sessions. They can be set using the export command:
```
export VARIABLE_NAME="value"
```
Persistent Environment Variables: These variables are stored in configuration files and are loaded automatically when a new shell session is started. The most common locations for persistent environment variables are:
- /etc/environment: System-wide environment variables
- ~/.bashrc or ~/.bash_profile: User-specific environment variables
To set a persistent environment variable, you can add the export command to the appropriate configuration file:
```
## Add this to ~/.bashrc or ~/.bash_profile
export VARIABLE_NAME="value"
```
Default Environment Variables: The Linux system provides a set of default environment variables, such as PATH, HOME, and USER, which are essential for the proper functioning of the operating system and applications.

Managing Environment Variables

Managing environment variables involves various tasks, such as:

Viewing Environment Variables: You can use the env or printenv commands to display all the environment variables currently defined in the system.
Modifying Environment Variables: You can update the value of an existing environment variable using the export command, or remove a variable using the unset command.
Temporary vs. Persistent Changes: When you set an environment variable using export, the change is only effective for the current shell session. To make the change persistent, you need to add the export command to the appropriate configuration file.
Scoping Environment Variables: Environment variables can have different scopes, such as system-wide, user-specific, or application-specific. Understanding the scope of a variable is important to ensure it is accessible and effective for the intended use.

By mastering the techniques for defining and managing environment variables, you can effectively customize your Linux system, configure applications, and automate various tasks to improve productivity and efficiency.

Leveraging Environment Variables in Applications

Environment variables are not only useful for system-level configurations but also play a crucial role in the development and deployment of applications. By leveraging environment variables, developers can create more flexible, configurable, and portable applications.

Environment Variables in Shell Scripts

Shell scripts are a common use case for environment variables. By using environment variables, you can make your scripts more adaptable and reusable. For example:

#!/bin/bash

## Use an environment variable to specify the application's configuration file
CONFIG_FILE="${MY_APP_CONFIG:-/etc/myapp/config.ini}"

## Use the variable in the script
my_app --config $CONFIG_FILE

In this example, the script uses the MY_APP_CONFIG environment variable to determine the location of the configuration file. If the variable is not set, the script falls back to a default value.

Environment Variables in Docker

When running applications in Docker containers, environment variables are a popular way to configure the container's behavior. Docker provides several ways to set environment variables, including:

Dockerfile: You can set environment variables in the Dockerfile using the ENV instruction.
docker run: You can pass environment variables to the container using the -e or --env flag.
docker-compose: You can define environment variables in the environment section of the docker-compose.yml file.

Using environment variables in Docker allows for easier configuration and deployment of applications across different environments.

Environment Variables in Jenkins

Jenkins, a popular continuous integration and deployment tool, also heavily relies on environment variables. You can set environment variables in Jenkins at various levels, such as:

Global Environment Variables: These variables are available to all jobs and pipelines in Jenkins.
Job-level Environment Variables: These variables are specific to a particular job or pipeline.
Declarative Pipeline Environment Variables: These variables can be defined within the environment section of a Jenkins Declarative Pipeline.

By leveraging environment variables in Jenkins, you can make your build and deployment processes more flexible, maintainable, and adaptable to different environments.

By understanding how to use environment variables in applications, you can create more robust, configurable, and portable software that can adapt to different environments and user requirements.

Summary

Environment variables are named values that are accessible to the operating system and all the processes running on it. They serve as a way to store and retrieve configuration information, user preferences, and other data that can be used by the system and applications. Understanding the importance of environment variables, how to access and modify them, and leveraging them in applications are key skills for Linux users and developers. By mastering the use of environment variables, you can enhance system configuration, customize application behavior, and streamline automation and scripting tasks, making your Linux experience more efficient and productive.