ls

The command ls lists directory contents. A directory is a file that consists solely of a set of other files, like a folder.

There are several options you can add to this command such as -a, -r, -R, -X, and many more.

-a

This option will list all entries in a directory, even ones starting with . .

This option lists entries in reverse alphabetical order.

This option recursively lists the contents of all sub-directories inside this one.

This option lists entries sorted alphabetically by entry extension

This option gives you a more complete listing of all of the files along with owner and permsisions.

To use:

ls [option] [directory location]

If a directory location is not specified, it will use the current directory you are in.

For example:

ls -r /usr

Would output the files in /usr in reverse alphabetical order.