Time to type something and get an answer back.
The shape every command shares
Command lines all look the same:
name argument argument
The first word is the command — the name of the program you want to run. Everything after it is arguments: the material the command works on, separated by spaces.
echo hello
echo is the command. hello is the argument. Press Enter and the terminal prints:
hello
That is the whole grammar. Learn it once and every command you meet after this is just a new name and new arguments.
Quick check
In the line `mkdir photos`, which word is the command?
Spaces are the separator, so they matter
The splits your line on spaces. That is how it knows where the command ends and the arguments begin.
echo hello world
sends echo two arguments, hello and world. It prints them back joined by a space, so you see hello world and nothing looks unusual. But a command that expects exactly one argument will be confused by two.
Tip
When something you type has a space inside it — a file called my notes.txt, say — wrap it in quotes: "my notes.txt". The quotes tell the shell “this is one thing, do not split it”. A surprising share of beginner errors are one missing pair of quotes.
Quick check
You want one argument that contains a space. What do you do?
Try it
Type this and press Enter:
echo Hello, terminal
The terminal prints Hello, terminal and gives you a fresh . That fresh prompt is the terminal’s way of saying “done, next”.
Note
echo earns its keep later. In level 2 you will send its output into a file instead of onto the screen, which is how you create files with content in them without ever opening an editor.
Quick check
After a command finishes, the terminal shows a new prompt. What does that mean?