Problem with writing the output of kpsewhich to a file

Question

I create in my folder a file "blub.temp" and then tried out the following

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{shellesc}
%correct small bug in shellesc:
\protected\def\ShellEscape{\immediate\write18 }
\begin{document}

\ShellEscape{kpsewhich article.cls    >> blub.temp}

\immediate\write18{kpsewhich book.cls >> blub.temp}


\end{document}

When I compile this (pdflatex on miktex, texlive 2015, texlive 2016) without shell-escape I see messages like this in the log-file

 runsystem(kpsewhich book.cls >> blub.temp)...executed safely (allowed).

But blub.temp has no content.

When I compile with --shell-escape I see messages like

 runsystem(kpsewhich book.cls >> blub.temp)...executed.

and blub.temp contains the both pathes.

How can it be that the command is executed but does nothing when --shell-escape is not used? Can one correct this?

Edit

As confirmed on the texlive list, redirections (>, >>) don't work in restricted mode. So the question is if there is any other way to catch the output of kpsewhich (without pipes or --shell-escape) ...

Answer 1

What about Lua?

\documentclass{article}
\begin{document}
\directlua{
    local fp = io.popen("kpsewhich article.cls")
    local fh = io.open("blub.temp", "a")
    while true do
       local line = fp:read()
       if line == nil then
          break
       end
       fh:write(line, "\noexpand\n")
    end
    fh:close()
    fp:close()
}
\end{document}