Now, we'll take a quick look at the ls command. Very likely, you're already familiar with ls and know that typing it by itself will list the contents of the current working directory:

$ cd /usr
$ ls
X11R6      doc         i686-pc-linux-gnu  lib      man          sbin   ssl
bin        gentoo-x86  include            libexec  portage      share  tmp
distfiles  i686-linux  info               local    portage.old  src

By specifying the -a option, you can see all of the files in a directory, including hidden files -- those that begin with .. As you can see in the following example, ls -a reveals the . and .. special directory links:

$ ls -a
.      bin        gentoo-x86         include  libexec  portage      share  tmp
..     distfiles  i686-linux         info     local    portage.old  src
X11R6  doc        i686-pc-linux-gnu  lib      man      sbin         ssl