Special files
The files such as /dev/nul
Example
cmp file file > /dev/nul.
This file accepts any stream without growing in the size.
The size is always 0.
That is what ever is the answer of the comparision it always has the size 0.
The next file is /dev/tty
It is not the file representing the standard output, standard Err.
It is not used for writing . It is used whenever some statements are suppose to be redirected.