Code blocks which are set aside from the text indicate user input to the system. Commands that should be entered into a Unix shell are indicated by the directory where you should enter the command ('~' indicates your home directory) followed by '$', followed by the highlighted command to enter (do not enter the '$'), and possibly followed by example command output in black. For example, the following block indicates that you should type ls foo.*
while in your home directory and the expected output will be "foo.input" and "foo.output".
~$ ls foo.*
foo.input foo.output