1 - echo "this is a message to be stored in a file" then redirect its output to a file of your choice.

2 - run a command that performs a task and redirect both of its error and output to the trash.

3 - cat a file of your choice and get the last 3 lines of it.

• you may use tail with a suitable flag to do such a thing.

• you input a command and you get an output; what you have entered using your keyboard is called stdin and what get as an output is called stdout.

• if the command generated an error then the error output is called stderr.

• In very simple terms, file descriptor A.K.A fd is an integer number somewhere on the OS that represents every file that is opened by a process.

• /proc/PID/fd is the path which you can check FDs that belongs to a process where PID is the Process Identifier.

• We write shell scripts to automate our command line interface(CLI)

Bash scripts related to every session of this tutorial will be stored in isolated branches named after their session name.

You can access the main code and the challenge answer key related to every session at their own branch.