Answer by Rinzwind for Environment Variable for Username

$USER

will change it into your username.

Example

rinzwind@schijfwereld:~$ echo $USERrinzwind

There are more...

~$ cd /tmp:/tmp$ echo $HOME/home/rinzwind:/tmp$ echo $PWD/tmp$ echo $HOSTNAMEschijfwereld

To list the current values of all environment variables:

env

Keep in mind that variable names are case-sensitive

To expand on this. You can create your own too:

export var=value

will create $var with value.

$ export var=1111rinzwind@schijfwereld:~$ echo $var1111