Problem Statement

Rename:

This should be done twice:   once "here", i.e. in the current working directory and once in the filesystem root. It can be assumed that the user has the rights to do so. (In unix-type systems, only the user root would have sufficient permissions in the filesystem root.)

Let's start with the solution:

"input.txt" "output.txt" frename
"/input.txt" "/output.txt" frename
"docs" "mydocs" frename
"/docs" "/mydocs" frename.