OK lets decide first if we're going with a single or separate commands. There seems to be an even split on that preference, which I think can be summarised as these two options:
1. relpath¹; realpath; readlink 2. realpath² --relative --canon --link cheers, Pádraig. ¹ Other names suggested: relname ² Other names suggested: getpath, tao, getpathname p.s. I'm not sure it's worth worrying about the path/$PATH ambiguity in this context.
