Arguments

The arguments or parameters are extra information you are passing into the command. Use spaces to separate commands from the argument.

python3 hello.py

This runs the program “python3” with the argument “hello.py”

If you leave the space out and type

python3hello.py

…the computer will look for a command called python3hello. You must use spaces as separators on the command line.

To rename the file apple.txt to banana.txt, use the mv (move) command:

mv apple.txt banana.txt

The command is mv, the first argument is apple.txt and the second argument i banana.txt.

If you have a file called I am a file.txt you have a problem:

mv I am a file.txt banana.txt

…because your computer will try to rename the file called I — and that file probably doesn’t exist. You can fix this either using quotation marks or by “escaping” the space:

mv "I am a file.txt" banana.txt

If you’re going to study computer science, make your life easier and never put spaces (or other special characters) into filenames. Of course you can put fancy things into your filenames, but you can avoid a world of pain by sticking to numbers, lowercase letters, hyphen (-), underscore (_) and dot (.). For similar reasons, it’s usually simpler to keep everything lower case. For more detail, see the intro about file systems.

Sometimes you must use capital letters in filenames: if there’s a good reason (because the programming language you are using requires it) then of course, that’s what you do.