Environment variables are settings that control how programs and shells behave on a Linux system. These settings include things like the location of executable files, the path to libraries, and the current working directory. Environment variables are stored in a variety of places, depending on their scope. Some environment variables are global and can be accessed by all processes on the system, while other environment variables are local and are only available to a particular process.

User-Specific Environment Variables

User-specific environment variables are stored in a file called .bashrc in the home directory of the user. This file is a shell script that is executed every time the user logs in. The .bashrc file contains commands that set environment variables for the user's session.

To see the user-specific environment variables that are currently set, run the following command:

printenv

This command will print a list of all the environment variables that are currently set, along with their values.

System-Wide Environment Variables

System-wide environment variables are stored in a file called /etc/environment. This file is a text file that contains a list of environment variable settings. The /etc/environment file is used to set environment variables that are available to all processes on the system.

To see the system-wide environment variables that are currently set, run the following command:

cat /etc/environment

This command will print the contents of the /etc/environment file.

Process-Specific Environment Variables

Process-specific environment variables are stored in the memory of the process. These environment variables are only available to the process that created them. To see the process-specific environment variables that are currently set, run the following command:

env

This command will print a list of all the environment variables that are currently set for the current process, along with their values.

Setting Environment Variables

You can set environment variables using the export command. The export command takes two arguments: the name of the environment variable and the value of the environment variable. For example, to set the PATH environment variable to include the directory /usr/local/bin, you would run the following command:

export PATH=/usr/local/bin:$PATH

This command will add the directory /usr/local/bin to the PATH environment variable, which means that programs will now be able to find executable files in that directory.

Unsetting Environment Variables

To unset an environment variable, use the unset command. The unset command takes the name of the environment variable as its argument. For example, to unset the PATH environment variable, you would run the following command:

unset PATH

This command will unset the PATH environment variable, which means that programs will no longer be able to find executable files in the directories that were previously included in the PATH environment variable.

Conclusion

Environment variables are a powerful tool for controlling the behavior of programs and shells on a Linux system. By understanding how environment variables are stored and how to set and unset them, you can customize your system to your own needs.

Frequently Asked Questions

• Q: What are environment variables?
  A: Environment variables are settings that control how programs and shells behave on a Linux system. These settings include things like the location of executable files, the path to libraries, and the current working directory.

• Q: Where are user-specific environment variables stored?
  A: User-specific environment variables are stored in a file called .bashrc in the home directory of the user.

• Q: Where are system-wide environment variables stored?
  A: System-wide environment variables are stored in a file called /etc/environment.

• Q: Where are process-specific environment variables stored?
  A: Process-specific environment variables are stored in the memory of the process.

• Q: How do I set an environment variable?
  A: You can set an environment variable using the export command. The export command takes two arguments: the name of the environment variable and the value of the environment variable.