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Most commands have one or more options that you can add to change the command's behavior. Options typically consist of a single letter preceded by a hyphen. However, you can group single-letter options together or precede each with a hyphen to use more than one option at a time. For example, the following two uses of options for the ls command are the same:

 $ ls -l -a -t $ ls -lat

In both cases, the ls command is run with the -l (long listing), -a (show hidden dot files), and -t options (list by time).

Some commands include options that are represented by a whole word. To tell a command to use a whole word as an option, you typically precede it with a double hyphen (--). For example, to use the help option on many commands, you enter --help on the command line. Without the double hyphen, the letters h, e, l, and p would be interpreted as separate options. There are some commands that don't follow the double hyphen convention, using a single hyphen before a word, but most commands use double hyphens for word options.