Using TeX to merge \input from top level files

This is silly. There are better ways to do it. Still, it was sort of fun to write.

\endlinechar=-1
\newread\in
\newwrite\out
\message{Please enter input file name: }
\read16to\inname
\openin\in=\inname \relax
\ifeof\in
        \immediate\write16{Failed to open \inname.}
        \expandafter\end
\fi
\message{Please enter output file name: }
\read16to\outname
\immediate\openout\out=\outname \relax
\begingroup
\catcode`@0
\catcode`(1
\catcode`)2
\catcode`\{12
\catcode`\}12
\catcode`I12
\catcode`N12
\catcode`P12
\catcode`U12
\catcode`T12
\catcode`\\12
@lowercase(
        @gdef@dosplitline#1\INPUT{#2}#3@splitsentinal(@def@ante(#1)@def@file(#2)@def@post(#3))
        @gdef@splitline(@expandafter@dosplitline@line\INPUT{@sentinal}@splitsentinal)
)
@endgroup
\def\splitpost{\expandafter\dosplitline\post\splitsentinal}
\def\sentinal{\sentinal}
\catcode`\%12
\def\processline{
        \ifx\file\sentinal
                \immediate\write\out{\ante}
                \let\temp\relax
        \else
                \immediate\write\out{\ante%}
                \let\temp\processline
                \copyfile
                \splitpost
                \ifx\empty\ante
                        \ifx\file\sentinal
                                \let\temp\relax
                        \fi
                \fi
        \fi
        \temp
}
\newread\f
\def\copyfile{
        \openin\f=\file\relax
        \ifeof\f
                \immediate\write16{Failed to open \file. Continuing.}
        \else
                \begingroup
                \loop
                        \readline\f to\line
                        \unless\ifeof\f
                        \immediate\write\out{\line}
                \repeat
                \endgroup
                \closein\f
        \fi
}

\loop
        \readline\in to\line
        \unless\ifeof\in
        \splitline
        \processline
\repeat
\closein\in
\immediate\closeout\out
\end