Practice Exercise: Understanding Environment Variables

Objective:

Explore environment variables in a Linux system and learn how to manage and utilize them effectively.

Task 1: Displaying Environment Variables

Open a terminal window.
Use the env command to display a list of all environment variables currently set on your system.

Identify common environment variables like PATH, HOME, USER, and SHELL. Take note of their values.

[intern@intern-a1t-inf-lnx1 ~]$ env
SHELL=/bin/bash
PWD=/home/intern
LOGNAME=intern
XDG_SESSION_TYPE=tty
MOTD_SHOWN=pam

Task 2: Creating Custom Environment Variables

Create a new environment variable named MY_VARIABLE and set it to your name or any custom value using the export command.

Use the env command again to verify that your new environment variable MY_VARIABLE has been added to the list.

[intern@intern-a1t-inf-lnx1 ~]$ export MY_VARIABLE=variable_value
[intern@intern-a1t-inf-lnx1 ~]$ env | grep MY_VARIABLE
MY_VARIABLE=variable_value

Task 3: Modifying Environment Variables

Change the value of the MY_VARIABLE environment variable to something else using the export command.
Verify that the value of MY_VARIABLE has been updated using the env command.

Try modifying one of the common environment variables, such as PATH or PS1, temporarily and observe the changes.

[intern@intern-a1t-inf-lnx1 ~]$ export MY_VARIABLE=variable_value2
[intern@intern-a1t-inf-lnx1 ~]$ env | grep MY_VARIABLE
MY_VARIABLE=variable_value2
[intern@intern-a1t-inf-lnx1 ~]$ export PATH=/home/projects
[intern@intern-a1t-inf-lnx1 ~]$ env | grep PATH
Command 'grep' is available in the following places
 * /bin/grep
 * /usr/bin/grep
The command could not be located because '/usr/bin:/bin' is not included in the PATH environment variable.
grep: command not found
Command 'env' is available in the following places
 * /bin/env
 * /usr/bin/env
The command could not be located because '/bin:/usr/bin' is not included in the PATH environment variable.
env: command not found

As you can see by changing the PATH value the command env and grep can't be located

The easiest way I can think of to fix it is to simply logout and login again.

[intern@intern-a1t-inf-lnx1 ~]$ env | grep PATH
PATH=/home/intern/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin

Of course this login and logout will also result in your MY_VARIABLE not persisting
Verify that MY_VARIABLE has been removed from the list of environment variables.
```
[intern@intern-a1t-inf-lnx1 ~]$ env | grep MY_VARIABLE
```

You can remove a environment variable as well by simply using the command unset

[intern@intern-a1t-inf-lnx1 ~]$ export MY_VARIABLE=variable_value
[intern@intern-a1t-inf-lnx1 ~]$ env | grep MY_VARIABLE
MY_VARIABLE=variable_value
[intern@intern-a1t-inf-lnx1 ~]$ unset MY_VARIABLE
[intern@intern-a1t-inf-lnx1 ~]$ env | grep MY_VARIABLE

Task 4: Using Environment Variables

Use the echo command to display the value of the HOME environment variable.
```
[intern@intern-a1t-inf-lnx1 ~]$ echo $HOME
/home/intern
```
Yes, to expand variables in linux you need the $
Create a simple shell script that utilizes environment variables to print a customized greeting message based on the USER environment variable.
```
# You can use your preffered editor
[intern@intern-a1t-inf-lnx1 ~]$ vi user.sh
```
With the following content
```
#!/bin/bash
echo "Hello $USER"
```
Don't worry if you don't understand some part of the script yet as we will discuss it in the shell scripting chapter

Execute the script and take note of the output

[intern@intern-a1t-inf-lnx1 ~]$ /bin/bash user.sh
Hello intern

Conclusion:

In this lab exercise, you've gained practical experience with environment variables in a Linux environment. You've learned how to display, create, modify, and use environment variables both in the terminal and within shell scripts. Understanding environment variables is essential for configuring and customizing your Linux system.