Spaces on the command line

All the spaces on the command line get squashed (collapsed) into single spaces. They are not commands themselves, but they serve as separators between commands.

If you type a few spaces at the prompt, you’ll see the cursor move along. (If there wasn’t a cursor, you wouldn’t be able to see this happening).

If you type a few spaces, type pwd and some more spaces, and then press enter…

…the pwd command runs (it prints the current working directory).

The command line interpreter collapses and strips the spaces, and looks for the command that is left.

Collapsing spaces means a run of spaces get squashed down to just one.
Stripping spaces means the spaces at the start and end get removed.

If you just type some spaces on the command line and press enter… nothing happens. The spaces are being collapsed and stripped to nothing: there’s no command.