sorting and reversing lines of a file

[Guy Harris]

>All you need is a smart cat ( :-); this one will probably do an
>fstat(2) (on 1), which not all Unixes (Unices ?) support.

What is it that not all UNIXes support?  All the ones I know of support
"fstat", and both 4.xBSD and S5 (and, as I remember, all versions going
back to V7) supported "cat" checking whether its output was the same
file as any of its inputs.