Commands
VS
The Shell
What really happens when we type a command? To understand this, we need to know the difference between a command and something called The Shell. Commands are just text but when you press enter the meaning of that text is interpreted by a computer program called The Shell. When a command is typed and entered, it is the Shell that interprets it and decides what to do with it. We now understand the difference between command and shell, what is the terminal then? A terminal is nothing more than just a window into the shell. To understand it better, let’s think about it; How would we type commands onto the shell without opening a terminal? We couldn’t! That is exactly what the terminal is. It is a middle piece between commands and the shell.
There are different types of shells and they interpret commands in different ways. There is one type of shell that is the most common shell, it’s called Bash Shell.
Important* Commands are actually case sensitive so if you type a command all uppercase if the shell isn’t expecting that command in uppercase it would give an error.