documentclass{article}
usepackage{fancyvrb}
newwriteFILE
immediateopenoutFILE=jobname.out

newenvironment{chunk}{%
    VerbatimEnvironment{chunk}begin{SaveVerbatim}[gobble=2,commentchar=%,commandchars=\{}]{VERB}%
}{%
  end{SaveVerbatim}%
  UseVerbatim{VERB}%
  immediatewriteFILE{UseVerbatim{VERB}}%
}

begin{document}

begin{chunk}
  First line.
  texttt{Second} line.
end{chunk}

end{document}