[pdftex] Access value of output-directory

[Johannes Burtscher]

   It could be done. But what do you want to do with the value?

I only recently wrote a small package for a co-worker and had to
rely on an external tool and shell-escape. In such a case it would
be very convenient to know whether the user wants all newly created
files in another directory or not. (To be honest, this is the only
use case where I can imagine beeing in need of this value).
I also found it rather awkward that I can read files from the
output-directory whereas \pdffilemoddate, for example, has no idea
where to find them.

   ... Although it's clear that "a lot of authors" don't need the
   output-directory value, since it has never been available at the TeX
   level -- yours is the first request I remember ever seeing, anywhere.

"A lot of authors" was certainly exaggerated but every now and then
such a question pops up:

- http://tex.stackexchange.com/q/136012/10350
- http://tex.stackexchange.com/q/294931/10350

In fact, the first question mentions a request posted right here on
this mailing list.


Regards,
Johannes