How do I delete an exported environment variable?

How to Delete Exported Environment Variables in Linux

Learn the essential commands and techniques to effectively remove or unset environment variables in your Linux shell, ensuring a clean and predictable environment.

Environment variables are dynamic named values that can affect the way running processes behave on a computer. In Linux, they are crucial for configuring your shell, applications, and system paths. While exporting a variable makes it available to child processes, there often comes a time when you need to remove or 'unset' these variables. This article will guide you through the process of deleting exported environment variables, explaining the unset command and its implications.

Understanding Environment Variables and Their Scope

Before deleting, it's important to understand what an environment variable is and its scope. When you define a variable in your shell, it's typically local to that shell session. Using the export command promotes it to an environment variable, making it accessible to any child processes launched from that shell. However, this export is usually temporary, lasting only for the duration of the current shell session. If you want a variable to persist across sessions, you typically add it to a shell configuration file like ~/.bashrc, ~/.zshrc, or ~/.profile.

flowchart TD
    A[Define Variable] --> B{Export?}
    B -- No --> C[Local to Shell]
    B -- Yes --> D[Environment Variable]
    D --> E[Available to Child Processes]
    E --> F{Shell Session Ends?}
    F -- Yes --> G[Variable Lost]
    F -- No --> D
    G --> H[Start New Session]

Lifecycle of an environment variable in a shell session.

Using the unset Command

The primary command for removing an environment variable is unset. This command removes a variable or function name from the shell environment. Once a variable is unset, it will no longer be available to the current shell or any new child processes launched from it. It's a straightforward command with a simple syntax.

# First, let's define and export a variable
export MY_VARIABLE="Hello World"

# Verify it's set
echo $MY_VARIABLE

# Now, unset it
unset MY_VARIABLE

# Verify it's gone
echo $MY_VARIABLE

Demonstrating the unset command.

Deleting Persistent Environment Variables

If you've made an environment variable persistent by adding it to a shell configuration file (e.g., ~/.bashrc, ~/.profile), simply using unset in your current terminal session will only remove it temporarily. To permanently delete such a variable, you need to edit the configuration file itself. After editing, you'll need to either source the file or open a new terminal session for the changes to take effect.

1. Identify the Configuration File

Determine which shell configuration file contains the variable definition. Common files include ~/.bashrc, ~/.zshrc, ~/.profile, or /etc/environment for system-wide variables.

2. Edit the File

Open the identified configuration file using a text editor (e.g., nano, vim, gedit). Look for lines that define or export your variable, such as export MY_VARIABLE="value" or MY_VARIABLE="value".

3. Remove or Comment Out the Line

Delete the line(s) defining the variable, or comment them out by placing a # at the beginning of the line. Commenting out is often preferred for temporary disabling or future reference.

4. Save and Exit

Save the changes to the file and exit your text editor.

5. Apply Changes

To apply the changes to your current shell session, run source ~/.bashrc (or the relevant file). For system-wide changes or to ensure a clean slate, it's often best to open a new terminal session.

# Example: Editing ~/.bashrc

# 1. Open the file
nano ~/.bashrc

# 2. Find and delete/comment out the line:
# export MY_PERSISTENT_VAR="some_value"

# 3. Save and exit (Ctrl+O, Enter, Ctrl+X in nano)

# 4. Source the file to apply changes to current session
source ~/.bashrc

Steps to remove a persistent environment variable from ~/.bashrc.