Access value of -output-directory

Question

I am considering using the command line option -output-directory=<some/path> so that the temporary files do not clog my working directory but are also available for subsequent builds. This will also eliminate a lot of unnecessary Dropbox activity.

However, I also produce some temporary files of my own, so would like to be able to access what the output-directory was specified as on the command line.

So, in the MWE below, how do I set the value of the macro \OuptutDirectory so that I can correctly determine the names of my temporary files?

References:

• Prevent pdflatex from writing a bunch of files
• Is there a way to configure pdflatex to make all but the .tex and .pdf files hidden files?

Related Question:

• Possible Issues of using -output-directory

Code:

\documentclass[a4paper]{article}
\def\OuptutDirectory{????}% <--- How do I determine this?
\edef\MyTempFile{\OuptutDirectory/\jobname.foo}%
\begin{document}
    My temp file is \MyTempFile.
\end{document}

Answer 1

I set up, in a working directory, the file a.tex containing

\newwrite\test
\immediate\openout\test=temp.txt

\immediate\write\test{Hello}

\bye

I created a temp subdirectory and called

pdftex -output-dir=temp a

and the temp.txt file was created in the temp directory:

> ls -R .
a.tex   temp/

./temp:
a.log       temp.txt

There's no variable that can be accessed from within pdftex that holds the output directory path, as far as I know.

Of course you can emulate it by passing the definition of \OutputDirectory from the command line:

pdftex -output-dir=temp "\def\OutputDirectory{./temp}\input a"

Answer 2

New solution starting from TeX Live 2024 ($TEXMF_OUTPUT_DIRECTORY)

Just access the environment variable named $TEXMF_OUTPUT_DIRECTORY. Use sys_get_shell: https://tex.stackexchange.com/a/62032/250119 . Credit: https://tex.stackexchange.com/a/707351/250119 .

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Solution using currfile-abspath

Using currfile-abspath detailed in https://tex.stackexchange.com/a/54894/250119 (see the note regarding -recorder flag), it's possible to use \currfileabsdir to get the output directory, using the facts that

• Writing to a file will write it to the output directory by default
• \input searches in the current -output-directory first

%! TEX program = xelatex
\documentclass{standalone}
\usepackage[abspath]{currfile}
\begin{document}
\ExplSyntaxOn
% write the content to a temporary file test.tex
\iow_new:N \myfile
\iow_open:Nn \myfile {test.tex}
\iow_now:Nn \myfile {
    \tl_set:Nx \myoutputdir {\currfileabsdir}
}
\iow_close:N \myfile
% execute the content of that file
\input {test.tex}
% print the obtained output directory path to the PDF
\texttt{\myoutputdir}
\ExplSyntaxOff
\end{document}

It does require a temporary file, however.

Note that if in one compilation there is -recorder, then in the following compilation there's no -recorder, I think it's impossible to detect the change --
currfile-abspath package gets it wrong as well.
Attempting to write to \jobname.fls might do something, but on Windows I think multiple write to the same file is not allowed.
One option is to randomize the file name, but that does not work on MiKTeX (recorder file not updated online) and clutters the file system.

Note that you may want to rename test.tex to something sufficiently obscure, and possibly check if the file exists before writing. If you're not careful you might overwrite some important file.

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Alternative using ps to get current process's command-line arguments

(because of some permission issue this does not work on Overleaf, but otherwise should work on most POSIX systems)

\ExplSyntaxOn
\sys_get_shell:nnN {ps~-o~args=~-p~$(ps~-o~ppid=~-p~$$)} {\cctab_select:N \c_other_cctab} \l_data_tl
\ExplSyntaxOff

Then \l_data_tl consist of the command-line of the TeX process (e.g. pdflatex --output-directory=/a/b/c main.tex) but note that all the characters will have "other" catcode including spaces.

From this, parsing the string to get the output directory is a standard exercise. Note that the relevant flag might be written as...

-output-d=/path
-output-d=
-output-dir=/path
--output-dir=/path
--output-directory=/path
-output-d /path
-output-directory /path
--output-directory /path

As far as I can tell these are all the variants (all prefixes of output-directory longer than or equal to output-d are accepted), although I haven't checked with e.g. texdoc pdftex-changes.

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Another alternative using find to look for the log file

Refer to David Carlisle's answer. Not recommended.

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Another alternative

(completely untested)

if you don't have -recorder, first write the file then refer to How to obtain absolute path of a file (or maybe file_get_full_name function in expl3, I'm not sure) to get the path of the file. (although this might fail, output-directory is not necessarily searched in by kpsewhich)

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Related answers:

• If you only need to read the file from TeX (instead of an external command) normal \file_get:nnN or \input works.
• If the output directory is in an environment variable (see this comment), you don't need to pass the output directory in a command, it's also possible to read the environment variable directly.
• For LuaTeX there's a direct solution: In Luatex, how to know effective output directory?
• Hard code both the path to write the file to and the path to read the file from (requires openout_any=a environment variable)
• Use scontents so you don't need a temporary file at all, refer to https://tex.stackexchange.com/a/513810/250119