How to Unset Environment Variable in Linux?

Using the Unset Command to Remove Variables

The unset command removes environment variables in Linux. The basic syntax is:

unset VARIABLE_NAME

Examples:

1. Remove a single variable:

   unset MY_CUSTOM_VAR

2. Remove multiple variables:

   unset VAR1 VAR2 VAR3

3. Remove an array variable:

   unset MY_ARRAY[2]

Using Export Command with Empty Values

The export command can unset variables by assigning an empty value:

export VARIABLE_NAME=

This method:

• Sets the variable to an empty string instead of removing it
• Keeps the variable defined but empty

Use export for unsetting variables when:

• You want to keep the variable defined but empty
• You need to override a variable in a child process

Modifying Configuration Files for Permanent Changes

For permanent changes, edit the configuration files:

1. User-specific changes: Edit ~/.bashrc or ~/.bash_profile:

   nano ~/.bashrc

   Remove or comment out the line setting the variable.

2. System-wide changes: Edit /etc/environment or create a file in /etc/profile.d/:

   sudo nano /etc/environment

   Remove the line setting the variable.

When modifying these files:

• Be careful as changes can affect system behavior
• Make a backup before editing
• Source the file or log out and back in for changes to take effect

Checking Current Environment Variables

To view your environment variables, use the env command:

env

This lists all environment variables and their values.

To display a specific variable's value, use the echo command:

echo $VARIABLE_NAME

Example:

echo $HOME

To search for specific variables, combine env with grep:

env | grep PATTERN

Example to find PATH-related variables:

env | grep PATH

Setting and Unsetting Variables for Different Users

Root users can change system-wide settings, while regular users can modify their own variables.

To modify variables for a specific user account:

1. Log in as that user
2. Edit their ~/.bashrc or ~/.bash_profile file
3. Add or remove variable declarations

For system-wide variable management:

1. Log in as root or use sudo
2. Edit /etc/environment or create a file in /etc/profile.d/
3. Add or remove variable declarations

User-specific changes only affect that user, while system-wide changes impact all users.

Environment Variables in SSH Connections

When connecting via SSH, some variables may not be preserved. To handle variables during remote connections:

1. Use the -o SendEnv option with ssh to send specific variables:

   ssh -o SendEnv=VAR1,VAR2 user@host

2. Configure the SSH server to accept these variables by editing /etc/ssh/sshd_config:

   AcceptEnv VAR1 VAR2

To remove variables over SSH, unset them in the remote session or modify the files on the remote system.

If you have variable-related issues in remote sessions:

1. Check if the variable is set locally: echo $VARIABLE_NAME
2. Verify if it's being sent: ssh -v user@host
3. Confirm if the SSH server is set to accept the variable
4. Check for settings in the remote user's shell files

Using Shell Scripts for Variable Control

Shell scripts help manage environment variables in Linux systems. You can create scripts to set, unset, or modify variables automatically.

To create a script for variable management:

1. Open a text editor and create a new file with a .sh extension
2. Add commands to manage variables
3. Save the file and make it executable with chmod +x script_name.sh

Example script to unset multiple variables:

#!/bin/bash

# List of variables to unset
variables=(VAR1 VAR2 VAR3)

# Loop through the list and unset each variable
for var in "${variables[@]}"
do
    unset $var
    echo "Unset $var"
done

Automating variable unset processes with scripts allows you to:

• Unset multiple variables at once
• Apply variable management across systems
• Modify variable management logic as needed

Advantages of script-based variable management include:

• Reproducibility: You can run the same script on multiple systems
• Version control: Scripts can be stored in version control systems
• Documentation: Scripts serve as documentation for variable management processes

Leveraging Configuration Management Tools

Configuration management tools provide a way to manage environment variables across multiple systems.

These tools allow you to:

• Define variables in a central configuration
• Apply variable changes across multiple servers
• Track changes to variable configurations over time

Benefits of using configuration management tools for variable management:

• Consistency: Apply the same variable settings across all systems
• Scalability: Manage variables on many servers
• Audit trail: Track who made changes to variable configurations and when

Popular configuration management solutions include:

1. Ansible: Uses YAML files to define configurations and can manage variables across systems
2. Puppet: Provides a language for defining configurations, including variable management
3. Chef: Uses Ruby-based recipes to manage configurations and variables

Example of managing variables with Ansible:

---
- hosts: all
  vars:
    my_variable: "example value"
  tasks:
    - name: Set environment variable
      ansible.builtin.lineinfile:
        path: /etc/environment
        line: "MY_VARIABLE={{ my_variable }}"
        state: present

    - name: Unset environment variable
      ansible.builtin.lineinfile:
        path: /etc/environment
        regexp: "^MY_VARIABLE="
        state: absent

This Ansible playbook sets and unsets an environment variable on all target hosts.