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Here, we're storing a directory name in a variable, and using the 
ls
 command 
against it to list the contents of it. This may seem relatively useless, but when you're 
scripting, this will save you time. Anytime you need to refer to something more than 
once, it should be in a variable. That way, in a script, you can change the contents of 
that variable just one time and everywhere in the script will reference it.
There are also variables that are automatically present in your shell that you did not 
explicitly set yourself. Enter this command for fun:
env
Wow! You should see a lot of 
variables, especially if you enter it in a desktop version 
of Ubuntu. 
These variables are set by the system, but can still be accessed via 
echo
 as you 
would any other. Some notable ones include 
$SHELL
 (stores the name of the binary 
that currently handles your shell), 
$USER
 (stores your current username), and 
$HOST
 
(stores the hostname for your device). Any of these variables can be accessed at any 
time, and may even prove beneficial in scripts.
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