Error using \usepackage{fancyvrb, fancybox}

Question

With TeX Live 2009, with this MWE.

\documentclass{article}
\usepackage{fancyvrb, fancybox}  
\begin{document}
    \begin{Verbatim}[frame=single]
      auto eth0
    \end{Verbatim}
\end{document}

I get the following error when compiling

Runaway argument?
      auto eth0^^M    \end{Verbatim}^^M^^M\end{document} ! File ended while scanning use of \Verbatim. <inserted text> 

Using

\usepackage{fancybox, fancyvrb}

makes the error go away, but it is disturbing. I assume that fancyvrb depends on fancybox, but the packages don't handle this gracefully. This took me a while to track down. For reference, I was looking at Peter Flynn's example in http://groups.google.com/group/latexusersgroup/browse_thread/thread/c8c2e5dd1e9ff5cf

The message in question starts with

I don't understand the problem. What I wrote works in any class. Just copy and paste it into a report.

and his example has those packages loaded in that order, to be precise \usepackage{fancyvrb,fancybox,calc}. So my question is, what is going wrong here precisely, and how can I effectively debug these kinds of issues in the future?

UPDATE: The choice between's Enrico's solution and Werner's solution was basically a tossup. I did like Enrico's identification of a problem with the fancybox Verbatim environment. However, I still am not clear how one can efficiently identify these problems when they crop up. If anyone has debugging tips, I'd like to hear them.

Answer 1

You should have noticed that in Peter Flynn's message the syntax used is

\begin{Verbatim}{frame=single}

and not

\begin{Verbatim}[frame=single]

This makes quite a big difference. Moreover, the Verbatim environment as redefined by fancybox seems not to like blank spaces in front of \end{Verbatim}: the following input

\documentclass{article}
\usepackage{fancybox}
\begin{document}
\begin{Verbatim}{frame=single}
   auto eth0
 \end{Verbatim}
\end{document}

raises the

Runaway argument?
{frame=single}^^M   auto eth0^^M \end{Verbatim}^^M\end{document}^^M
! File ended while scanning use of \FV@BeginScanning.

error.

Of course, both packages trying to redefine \VerbatimEnvironment is not very helpful to the user. However, if you load fancyvrb as second, you get all of its functionality, without losing fancybox's as regards to boxes and frames. The implementation of the verbatim environments in fancybox seems buggy (the requirement that \end{Verbatim} starts on column 1 is surely a bug), so I believe it's best to say

\usepackage{fancybox,fancyvrb}

Answer 2

The problem here is that both packages define internal commands that are very similar, yet conflicting. For example, fancyvrb defines

\def\VerbatimEnvironment{%
  \ifx\FV@EnvironName\relax\xdef\FV@EnvironName{\@currenvir}\fi}

while fancybox defines

\def\VerbatimEnvironment{%
  \ifx\@VerbEnvir\relax\xdef\@VerbEnvir{\@currenvir}\fi}

Not to say that this is the root of the problem, but it is meant to illustrate the similarities between some of the definitions. As such, switching the load order of the packages could make the one package work, but not the other.

Why does the load order

\usepackage{fancybox,fancyvrb}

work? Well, because you only used functionality provided by fancyvrb making the load/use of fancybox unnecessary. Why does Peter's suggested solution work? Well, because he didn't need to load fancyvrb in the first place, since he only used fancybox functionality.

How come you were not alerted of conflicting commands until compilation? That's because many macro definitions and environments are constructed using TeX's \def rather than LaTeX's \newcommand. The latter automatically checks to see whether a command already exists and issues an error if it does, while the former happily overwrites a previous definition.

Perhaps this could be considered a partial incompatibility between the two packages - an incompatibility none the less.

Answer 3

The following works.

\documentclass{article}
\begin{document}
    \begin{verbatim}[frame=single]
      auto eth0
    \end{verbatim}
\end{document}