Working with Environment Variables on Linux

In Linux, environment variables are dynamic values that can affect the behavior of processes and programs. They are essentially key-value pairs that are accessible to all running processes. Here are some key points about Linux environment variables:

1. Setting Environment Variables:

• Temporary: You can set an environment variable for the current session in the terminal using the export command. For example:

export VARIABLE_NAME=value

• Permanent: To make an environment variable persistent across sessions, you can add it to the configuration files like '.bashrc', ‘.bash_profile‘, or ‘/etc/environment‘ depending on your shell.

2. Viewing Environment Variables:

• To view all environment variables, you can use the ‘printenv' command or ‘env'.
• To view a specific environment variable, use 'echo $VARIABLE_NAME‘.

3. Common Environment Variables:

• PATH: A list of directories where the system looks for executable files. Each directory is separated by colons (:) and it is in the format ‘PATH=/directory1:/directory2‘.
• HOME: This variable points to the current user’s home directory, typically /home/username.
• USER or LOGNAME: These variables store the current username.
• PS1: This variable sets the shell prompt.
• LANG or LC_ALL: These variables define the system’s default locale settings.

4. Modifying Environment Variables:

• To change the value of an environment variable in the current session, simply reassign it.

VARIABLE_NAME=new_value

• To permanently change an environment variable, you’ll need to edit one of the shell’s configuration files.

5. Special Environment Variables:

• $$: PID (Process ID) of the current shell.
• $?: Exit status of the last command.
• $0: The name of the current script or program.

6. Passing Environment Variables to Processes:

• You can pass environment variables to a process by defining them before the command. For example:

VARIABLE_NAME=value command

7. Creating Custom Environment Variables:

• You can create your own custom environment variables for specific applications or scripts. Simply set them as shown in point 1.

8. Removing Environment Variables:

• To remove an environment variable, you can use the unset command. For example:

unset VARIABLE_NAME

Remember that environment variables are case-sensitive and typically in uppercase. They play a crucial role in how your Linux system operates, and understanding how to manage them can be important for configuring your environment to suit your needs.