Introduction
Environment variables are a fundamental aspect of operating system interaction within shell environments like Bash on Linux or macOS. They allow users to store data that can influence the behavior of processes running in their session. This tutorial will guide you through creating, exporting, checking, and deleting environment variables efficiently.
Creating and Exporting Environment Variables
In Bash, an environment variable is simply a named value accessible by processes initiated from the shell. To create one:
DUALCASE=1
export DUALCASE
The export command makes DUALCASE available to subprocesses of your shell.
Checking for Existence
To verify if an environment variable exists, use:
env | grep DUALCASE
If the output shows the variable, it confirms its presence. An empty result indicates the absence of the variable in the current environment scope.
Deleting Environment Variables
The unset command is utilized to remove variables from your session:
unset DUALCASE
After running this, checking with env | grep DUALCASE will return an empty output if successful.
Clearing Local and Exported Variables
Unsetting Local Variables
Local shell variables can be reset by restarting the shell session or using:
CAN="chuck norris"
set | grep CAN # Shows variable set locally
exec bash # Resets local variables
exec bash clears all shell-local variables without touching exported ones.
Unsetting Environment Variables
For environment variables, you can clear them with:
export DOGE="so wow"
env -i bash # Start a new shell session with no environment variables
The env -i bash command initializes a new Bash instance devoid of any previous environment settings.
Permanently Removing Environment Variables
To remove an environment variable beyond the current session:
On Linux/macOS
Edit your shell’s profile script, usually located at ~/.bashrc or /etc/profile.d/*.sh, and remove the export line associated with the variable. After saving changes, reload the configuration using:
source ~/.bashrc
On Windows
The command to delete an environment variable is:
setx GNUPLOT_DRIVER_DIR ""
Using Different Shells: C Shell Example
For users of csh or tcsh, environment variables are managed differently. To create a variable with automatic export, use:
setenv x "something"
To delete it, utilize:
unsetenv x
For variables set without the automatic export feature:
set x = "something"
unset x
Best Practices
- Consistency: Stick to one method of setting environment variables for clarity.
- Documentation: Keep a note or comment within your profile scripts on what each variable does, especially if it’s crucial for system processes.
By mastering these commands and practices, you will be able to effectively manage the configuration of your shell environments across different platforms and shells. Whether for development, scripting, or general task automation, environment variables play a pivotal role in customizing and controlling your command-line experience.