gistfile1.txt

\documentclass{article}
\usepackage{listings} 

\begin{document}
\lstinputlisting[numbers=left,firstline=4,lastline=6]{sandbox.tex}   
\end{document}

% this gives me smth like that:
% 
% 
% 1 \begin{document}
% 2 \lstinputlisting[numbers=left,firstline=4,lastline=6]{sandbox.tex}   
% 3 \end{document}
%
% and not...
% 
% 4 \begin{document}
% 5 \lstinputlisting[numbers=left,firstline=4,lastline=6]{sandbox.tex}   
% 6 \end{document}