The Structure of a Unix command-line

In the previous lesson, you were introduced to three main commands, and you saw some examples of using ls (list) and cd (change directory) with options (flags) and arguments. This lesson takes a deeper dive into options and arguments, clarifying the differences and providing examples:

Arguments and Options

A command is like a verb.
Arguments are like objects of a verb.
Options (flags) are like adjectives: they modify the command.

cd (change directory) typically requires an argument: what directory do you want to change to?
ls (list) can take an argument (the directory you want to list), but also has options (a.k.a. flags): -l make it a long listing, -a list all the files and folders, including hidden ones. Note that flags are preceded by a dash, or sometimes two dashes. Arguments are NOT preceded by a dash.

cd and the special case of the home directory

Although cd typically requires an argument (where you want to go), there is a special case: If you type cd without an argument, it takes you to your home directory! Thanks to my student Alexe Delval for pointing out this inconsistency.

If you understand that there is a common structure to command lines, you'll be better able to make sense out of the long commands that are often necessary to specify which files you want as input, what you want as output, and how those files should be manipulated.

This 2.5-minute excerpt focuses on ls and also explains hidden files and folders.

Unix 2: Unix commands