Why doesn’t verbatim work within …?

The LaTeX verbatim commands work by changing category codes. Knuth says of this sort of thing “Some care is needed to get the timing right…”, since once the category code has been assigned to a character, it doesn’t change. So \verb and \begin{verbatim} have to assume that they are getting the first look at the parameter text; if they aren’t, TeX has already assigned category codes so that the verbatim command doesn’t have a chance. For example:

\verb+\error+

will work (typesetting \error), but if we define no more than a no-op macro,

\newcommand{\unbrace}[1]{#1}

which simply regurgitates its argument, and use it as:

\unbrace{\verb+\error+}

the combinartion will not (it will attempt to execute \error). Other errors one may encounter are “\verb ended by end of line”, or even the rather more helpful “\verb illegal in command argument”. The same sorts of thing happen with \begin{verbatim} … \end{verbatim}:

\ifthenelse{\boolean{foo}}{%
\begin{verbatim}
foobar
\end{verbatim}
}{%
\begin{verbatim}
barfoo
\end{verbatim}
}

provokes errors like ‘File ended while scanning use of \@xverbatim, as \begin{verbatim} fails to see its matching \end{verbatim}.

This is why the LaTeX book insists that verbatim commands must not appear in the argument of any other command; they aren’t just fragile, they’re quite unusable in any “normal” command parameter, regardless of \protection. (The \verb command tries hard to detect if you’re misusing it; unfortunately, it can’t always do so, and the error message is therefore not reliable as an indication of problems.)

The first question to ask yourself is: “is \verb actually necessary?”.

• If \texttt{_your text_} produces the same result as \verb+_your text_+, then there’s no need of \verb in the first place.
• If you’re using \verb to typeset a URL or email address or the like, then the \url command from the url will help: it doesn’t suffer from all the problems of \verb, though it’s still not robust; “typesetting URLs” offers advice here.
• If you’re putting \verb into the argument of a boxing command (such as \fbox), consider using the lrbox environment:

   \newsavebox{\mybox}
   ...
   \begin{lrbox}{\mybox}
     \verb!VerbatimStuff!
   \end{lrbox}
   \fbox{\usebox{\mybox}}
  

If you can’t avoid verbatim, the \cprotect command (from the package cprotect) might help. The package manages to make a macro read a verbatim argument in a “sanitised” way by the simple medium of prefixing the macro with \cprotect:

\cprotect\section{Using \verb|verbatim|}

The package does work in this simple case, and deserves consideration in many others cases; the package documentation gives more details.

Another way out is to use one of “argument types” of the \NewDocumentCommand command in the experimental LaTeX3 package xparse:

\NewDocumentCommand\cmd{ m v m }{#1 `#2' #3}
\cmd{Command }|\furble|{ isn't defined}

Which gives us: Command \furble isn’t defined The m tag argument specifies a normal mandatory argument, and the v specifies one of these verbatim arguments. As you see, it’s implanting a \verb-style command argument in the argument sequence of an otherwise “normal” sort of command; that | may be any old character that doesn’t conflict with the content of the argument.

This is pretty neat (even if the verbatim is in an argument of its own) but the downside is that xparse pulls in the experimental LaTeX3 programming environment (l3kernel) which is pretty big.

Other than the cprotect package, there are four partial solutions to the problem:

• Some packages have macros which are designed to be responsive to verbatim text in their arguments. For example, the fancyvrb package defines a command \VerbatimFootnotes, which redefines the \footnotetext command, and hence also the behaviour of the \footnote) command, in such a way that you can include \verb commands in its argument. This approach could in principle be extended to the arguments of other commands, but it can clash with other packages: for example, \VerbatimFootnotes interacts poorly with the para option of the footmisc package.

  The memoir class defines its \footnote command so that it will accept verbatim in its arguments, without any supporting package.

• The fancyvrb package defines a command \SaveVerb, with a corresponding \UseVerb command, that allow you to save and then to reuse the content of its argument; for details of this extremely powerful facility, see the package documentation.

  Rather simpler is the verbdef package, whose \verbdef command defines a (robust) command which expands to the verbatim argument given; the newverbs package provides a similar function as well as several related ones.

• In a similar vein, the verbatimbox package makes it possible to put verbatim material in a box:

   \begin{verbbox}
   some exotic _&$ stuff
   \end{verbbox}
   \theverbbox
  

  the operation typesets exotic stuff into an anonymous box, and its contents may be retrieved using the command \theverbbox. It is clear that it’s in the same mould as the \verbdef command mentioned above; the package defines other similar commands.

• The tcolorbox package provides a similar facility

• If you have a single character that is giving trouble (in its absence you could simply use \texttt), consider using \string. \texttt{my\string_name} typesets the same as \verb+my_name+, and will work in the argument of a command. It won’t, however, work in a moving argument, and no amount of \protection will make it work in such a case.

  A robust alternative is:

   \chardef\us=`\_
   ...
   \section{... \texttt{my\us name}}
  

  Such a definition is “naturally” robust; the construction “‹back-tick›\<char> may be used for any troublesome character (though it’s plainly not necessary for things like percent signs for which (La)TeX already provides robust macros).

• One may also consider putting verbatim material in an external file; this is somewhat more tedious, but the file may be reused several times within a single document. The tcolorbox package allows this:

   \begin{tcbverbatimwrite}{<file name>}
   ...
   \end{tcbverbatimwrite}
  

  which (as one might guess) writes to the named file; load the saved contents using \input{<file name>}

  A second environment puts your verbatim material in an (apparently) anonymous temporary file:

   \begin{tcbwritetemp}{<file name>}
   ...
   \end{tcbverbatimwrite}
  

  In this case, you use the anonymous file with the \tcbusetemp macro. (You can change the name used for the “anonymous” file, if its default proves troublesome.)

  The moreverb package provides a \verbatimwrite command, which doesn’t provide an anonynous file.

  Macros, to achieve the same effect, are outlined in the documentation of the verbatim package; the macros use the facilities of the package, but the user has to write a mini-package actually to use them.

FAQ ID: Q-verbwithin