Using listings with output

The best way to show the output along with the LaTeX code is to use the showexpl package:

Notes:

• To adjust the position of the output you can use the pos= option: top, bottom, right, left, outer, and inner.

Code:

%\RequirePackage{filecontents}% Comment out so that "example.tex" is not overwritten
\begin{filecontents*}{example.tex}
    Here is some \LaTeX code in an 
    \emph{external} file.  
    The input file is not altered in
    terms of line breaks, but the
    output is properly typeset.
\end{filecontents*}

\documentclass{article}
\usepackage{showexpl}
\usepackage{xcolor}

\lstset{ % General setup for the package
    language={[LaTeX]TeX},
    basicstyle=\small\sffamily,
    numbers=left,
    numberstyle=\tiny,
    frame=tb,
    tabsize=4,
    columns=fixed,
    showstringspaces=false,
    showtabs=false,
    keepspaces,
    commentstyle=\color{red},
    keywordstyle=\color{blue}
}

\begin{document}

Use the environment \verb|LTXexample| to show the code and its output:
\medskip
\begin{LTXexample}[width=0.60\linewidth]
\begin{document}
Welcome to \LaTeX.
\end{document}
\end{LTXexample}

\bigskip
To include code from an external file, use \verb|\LTXinputExample|, 
and also applied \verb|pos=r| to have output on right: 
\medskip
\LTXinputExample[width=0.5\linewidth,pos=r]{example.tex}

\end{document}

The tcolorbox provides means for nice typesetting and direct output of listings LaTeX code. There are many conceptual and visual configuration possibilities, see the documentation of tcolorbox, e.g. in chapter 9 of the current version 3.12.

However, a \begin{document}....\end{document} cannot be catched easily. Just relaxing \begin{document} etc. is no option. The document environment has to be redefined within a group, such that it's capsuled and does not influence the real outer document environment. However, this will drop some content defined within a potential \AtBeginDocument or \AtEndDocument.

In principle any command allowed only in Preamble will break this example.

---

\documentclass{article}
\usepackage{listings}
\usepackage{tcolorbox}
\tcbuselibrary{listings}%
\usepackage{xcolor}

\lstset{ % General setup for the package
    language={[LaTeX]TeX},
    basicstyle=\small\sffamily,
    numbers=left,
    numberstyle=\tiny,
    frame=tb,
    tabsize=4,
    columns=fixed,
    showstringspaces=false,
    showtabs=false,
    keepspaces,
    commentstyle=\color{red},
    keywordstyle=\color{blue}
}%



\tcbset{listing engine={listings}}
\begin{document}

% Redefine the document environment within a group
\begingroup
\renewenvironment{document}{%
  }{%
 }%

\begin{tcblisting}{}
\begin{document}
Welcome to \LaTeX.
\end{document}
\end{tcblisting}

\endgroup

\end{document}