Command line


One major benefit of using the command line is that you can give commands options. Compare this with clicking on an icon: you can’t easily click it differently in order to launch the program in a different way. But on the command line it’s very common to be able to add options that change the way the command runs.

Options let you give a command extra information about how you want it to run. They are called options because they are usually optional.

Arguments typically tell the command what, whereas options give extra information about how.

Options usually control how a command runs. They begin with a hyphen (-) immediately followed by a letter indicating which option it is. The hyphen is crucial: it’s how the computer knows it’s an option and not an argument.

Every command will have its own options. Some have none (but in Unix, this is unusual).

Some options just work by being there (these are the simplest ones to use).

Other options have a value associated with them.

A short option is one letter:


A long option is more than one letter, and has two hyphens


Often — but not always (it depends on the command or program) — the same option has both forms: short (for convenience) and long (for clarity). For example, -v and --version might both be the same option. But be careful because that’s not always the case!

The programs you write can accept options, but what they mean is up to you. Most programming languages have libraries to help you define and use your own.

It’s common to learn the useful options for the commands you use most. But you must know how to find others. On Unix, use the man (manual) command to see them.