TeX/stdout

\gdef\@missingfileerror#1#2{%

    \typeout{^^J! LaTeX Error: File `#1.#2' not found.^^J^^J%
     Type X to quit or <RETURN> to proceed,^^J%
     or enter new name. (Default extension: #2)^^J}%
    \message{Enter file name: }%
     {\endlinechar\m@ne
      \global\read\m@ne to\@gtempa}%
   \ifx\@gtempa\@empty
   \else
     \def\reserved@a{x}\ifx\reserved@a\@gtempa\batchmode\@@end\fi
     \def\reserved@a{X}\ifx\reserved@a\@gtempa\batchmode\@@end\fi
     \filename@parse\@gtempa
     \edef\filename@ext{%
       \ifx\filename@ext\relax#2\else\filename@ext\fi}%
    \edef\reserved@a{%
      \noexpand\InputIfFileExists
        {\filename@area\filename@base.\filename@ext}%
        {}%
        {\noexpand\@missingfileerror
           {\filename@area\filename@base}{\filename@ext}}}%
     \reserved@a
   \fi}