Unicode compatible version of \filename@parse?

Question

LaTeX contains an internal macro \filename@parse that decomposes a filename into path and basename. Applying it to a filename that contains unicode characters, in conjunction with pdflatex, does not work, however.

$ pdflatex test
...
> \filename@base=macro:
->\LGR\textalpha \LGR\texttau \LGR\textalpha .
l.6 \show\filename@base

where test.tex contains

\documentclass{article}
\usepackage[greek]{babel}
\begin{document}
\makeatletter
\filename@parse{ατα.tex}
\show\filename@base
\makeatother
\end{document}

\LGR\textalpha \LGR\texttau \LGR\textalpha apparently is not a proper filename.

Using xelatex or lualatex instead of pdflatex works, but requires to set up a Greek font separately. On the other hand, \input{ατα.tex} works also under pdflatex.

Is there an equivalent of \filename@parse that does not expand the Unicode characters? (Apparently babel defines them as macros.)

Answer 1

You can use \file_parse_full_name:nNNN (the expandable version, \file_parse_full_name:n, is used in the implementation of the current filename parsing in the kernel, used for example in \input). You can define a wrapper around \file_parse_full_name:nNNN, so that it works exactly like \filename@parse:

\documentclass{article}
\usepackage[greek]{babel}
\ExplSyntaxOn \makeatletter
\cs_new_protected:Npn \safe@filename@parse #1
  {
    \file_parse_full_name:nNNN {#1}
      \filename@area \filename@base \filename@ext
  }
\ExplSyntaxOff
\begin{document}
\makeatletter
\filename@parse{ατα.tex}
\show\filename@base
\safe@filename@parse{ατα.tex}
\show\filename@base
\makeatother
\end{document}

The terminal shows:

> \filename@base=macro:
->\LGR\textalpha \LGR\texttau \LGR\textalpha .
l.15 \show\filename@base

?
> \filename@base=macro:
->ατα.
l.17 \show\filename@base

?

---

Another option is to use \set@curr@file{<filename>} to normalise the file name to catcode 12 tokens, then you can safely use \filename@parse\@curr@file extract the parts you want:

\documentclass{article}
\usepackage[greek]{babel}
\begin{document}
\makeatletter
\set@curr@file{ατα.tex}
\filename@parse\@curr@file
\show\filename@base
\makeatother
\end{document}

Note that this approach will also follow file substitutions, if there are any set up for that filename.

Answer 2

I would simple detokenize the file name

\expandafter\filename@parse\expandafter{\detokenize{ατα.tex}}

Answer 3

Just as an exercise a regex version. Of course it is better to use \file_parse_full_name.

\documentclass{article}
\usepackage[greek]{babel}
\begin{document}
\ExplSyntaxOn
% list (sequence) variable and string (token list) variable
\seq_new:N \l_path_seq
\tl_new:N \l_base_name
% split on / and store in list
\regex_split:nnNTF { / } { /home/user/ατα.ch.tex } \l_path_seq { } { }
% store last token from list in \l_base_name
\seq_pop_right:NN \l_path_seq \l_base_name
% remove .ext
\regex_replace_once:nnN { \.\w+\Z } { } \l_base_name
\show\l_base_name
\ExplSyntaxOff
\end{document}

Result:

> \l_base_name=macro:
->ατα.ch.
l.14 \show\l_base_name

Answer 4

I suggest grabbing filenames from the .tex-input as verbatim-arguments (v-type in xparse) and to apply \detokenize.

• When grabbing as v-type-arguments you can have filenames with unbalanced curly braces and several consecutive spaces.
• v-type ensures that no hashes/no explicit character tokens of category 6(parameter) and no control-sequence-tokens are tokenized. (\detokenize would double hashes and append spaces behind control-word-tokens and the result of detokenizing control-sequence-tokens depends on the current value of \escapechar.)
• \detokenize in turn turns active characters into characters of category 12 and 10.
• Characters of category-code 10 not belonging to the name of a control symbol regardless their code-point number in the TeX-engine's internal character representation scheme always being tokenized as explicit character tokens of category 10 and character code 32 must be kept in mind.

\makeatletter
\NewDocumentCommand\PassTofilename@parse{+v}{%
  \expandafter\filename@parse\expandafter{\detokenize{#1}}%
}
\PassTofilename@parse"\relax#}  {ατα.tex"
\show\filename@base
\stop

Console-output on a utf8-shell:

$ pdflatex test.tex
This is pdfTeX, Version 3.14159265-2.6-1.40.21 (TeX Live 2020) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
(./test.tex
LaTeX2e <2020-10-01> patch level 4
L3 programming layer <2021-02-18>
> \filename@base=macro:
->\relax#}  {ατα.
l.6 \show\filename@base
                       
? 
 )
No pages of output.
Transcript written on test.log.