<i>&quot;On my Linux system cat has a -n option, which numbers the output lines. If it were following the &#x27;UNIX philosophy&#x27;, this option would not exist.&quot;</i><p>Gnu&#x27;s not Unix.  &quot;The GNU coreutils version of this on my Linux box behaves this way&quot; is not a good way of getting at finer points of what is or is not Unix-y.<p>That said, -n exists in BSD cat as well.  It&#x27;s not required by POSIX, though.