How to override a system environment variable?

Overriding System Environment Variables in Linux

In the Linux operating system, environment variables are a set of key-value pairs that provide information about the current working environment. These variables are used by the shell and various applications to configure their behavior. Sometimes, you may need to override the default system environment variables to customize the environment for your specific needs.

Understanding Environment Variables

Environment variables are stored in the shell's environment, which is a collection of key-value pairs that are accessible to all the processes and programs running in the shell. These variables can be used to store information such as the user's home directory, the system's PATH, and other configuration settings.

You can view the current environment variables by using the env or printenv command in the terminal:

env
# or
printenv

This will display a list of all the environment variables currently set in your shell.

Overriding System Environment Variables

To override a system environment variable, you can follow these steps:

1. Identify the Environment Variable: First, you need to identify the environment variable you want to override. You can use the env or printenv command to list all the environment variables and find the one you want to change.

2. Set the New Value: Once you have identified the environment variable, you can set a new value for it. You can do this by using the export command in the terminal:

   export VARIABLE_NAME="new_value"

   This will set the new value for the specified environment variable.

3. Verify the Change: After setting the new value, you can verify the change by using the env or printenv command again.

It's important to note that the changes made using the export command are only effective in the current shell session. If you want the changes to persist across sessions, you can add the export command to your shell's configuration file (e.g., .bashrc or .bash_profile) so that the new value is set every time you start a new shell.

Here's an example of overriding the PATH environment variable:

# Current PATH value
echo $PATH
# /usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

# Override the PATH variable
export PATH="/usr/local/bin:/opt/custom/bin:$PATH"

# Verify the new PATH value
echo $PATH
# /usr/local/bin:/opt/custom/bin:/usr/bin:/bin:/usr/sbin:/sbin

In this example, we first display the current PATH value, then override it by adding a new directory (/opt/custom/bin) to the beginning of the PATH variable. Finally, we verify the new PATH value.

Mermaid Diagram: Environment Variable Overriding

This diagram illustrates the process of overriding a system environment variable. The user shell has access to the system environment variables, and applications/processes running in the shell can also access these variables. To override a variable, the user can set a new value for the variable in the shell, which will then be used by the applications and processes running in that shell.

In summary, overriding system environment variables in Linux involves identifying the variable you want to change, setting a new value for it using the export command, and verifying the change. This allows you to customize the environment for your specific needs and ensure that your applications and processes use the desired configuration.