Get relative path to class file from inside the document class

Question

Is it possible to get the relative path used in the call to \documentclass so that I can use \input inside a document class, to import files relative to the .cls file?

Example folder structure:

./cls/class.cls
./cls/otherfiles/otherfile.tex
./document/document.tex

I use \documentclass{../cls/class} to import my class.

I'd like to use \input{otherfiles/otherfile} in my class.cls to easily separate some code blocks for better readability.

However, including the document class in ./document/document.tex leads to LaTeX Error: File otherfiles/otherfile.tex` not found..

Answer 1

Here's a macro to extract the path from the call to a class or package file. If your class file is test.cls, if you call \getrelativepath\thispath{test.cls} then the macro \thispath will contain the relative path used in \documentclass. If no relative path was used the macro will be empty, so you can safely use \input{\thispath otherfile.tex}. This command will only work when used inside a .cls or .sty file, as it relies on LaTeX's file handling code. If you use it in the document you'll get an error.

Here's the code. I put it in a filecontents environment to make it a working example. The second block is the bulk of the definition, and the third one is an example usage:

\begin{filecontents*}{test.cls}
\LoadClass{article}

\RequirePackage{expl3}
\ExplSyntaxOn
\str_new:N \l__carsten_tmpa_str
\cs_new_protected:Npn \__carsten_tmp:w { }
\cs_new_protected:Npn \getrelativepath #1 #2
  {
    \str_set:Nx \l__carsten_tmpa_str { \@currname.\@currext }
    \exp_args:NV \str_if_in:NnTF \l__carsten_tmpa_str {#2}
      {
        \str_if_eq:VnTF \l__carsten_tmpa_str {#2}
          { \tl_set:Nn #1 { } }
          { \exp_args:Nx \__carsten_parse_path:nN { \tl_to_str:n {#2} } #1 }
      }
      { \msg_error:nnxx { carsten } { wrong-path } {#2} { \l__carsten_tmpa_str } }
  }
\cs_new_protected:Npn \__carsten_parse_path:nN #1 #2
  {
    \cs_set_protected:Npn \__carsten_tmp:w ##1 #1 \q_mark ##2 ##3 \q_stop
      {
        \quark_if_nil:nTF {##2}
          { \tl_set:Nn #2 {##1} }
          { \msg_error:nn { carsten } { unexpected-error } }
      }
    \use:x
      {
        \__carsten_tmp:w
          \exp_not:V \l__carsten_tmpa_str \exp_not:n { \q_mark \q_nil }
                        \tl_to_str:n {#1} \exp_not:n { \q_mark \q_mark }
            \exp_not:N \q_stop
      }
  }
\msg_new:nnn { carsten } { wrong-path }
  { Unexpected~path~error.~'#1'~not~found~in~'#2'. }
\msg_new:nnn { carsten } { unexpected-error }
  { This~should~not~happen. }
\ExplSyntaxOff

\getrelativepath\thispath{test.cls}

\end{filecontents*}
\documentclass{../tex.sx/test}
\begin{document}

\texttt{\thispath}

\end{document}

On my system it prints: