[Tex/LaTex] How to escape properly and output regex in latex

text manipulationverbatim

Escaping regex is a heck of a work on LaTeX. How should I write in latex syntax such that I can output the following regexes:

^\(?\s?\w{1,5}\s*[):.]\s*

and

[\[\(].{1,}[\]\)]

I've tried \text{[\[\(].{1,}[\]\)]} but it gives compilation errors.

Best Answer

You can use a verbatim (fancyvrb package) or listings environnement.

\documentclass{article}
\usepackage{fancyvrb}
\begin{document}

\begin{Verbatim}[frame=single]
    ^(?\s?\w{1,5}\s*[):.]\s*
\end{Verbatim}

\end{document}

enter image description here

Related Solutions

[Tex/LaTex] fancyvrb alternate commandchars and \textcolor

The problem is that \textcolor expects an actual brace after it, not just a "group open" token: its definition is

\def\textcolor#1#{...}

(here #1 would be the possible "color model" allowed by the syntax). You can do with another command defined in terms of \textcolor:

\newcommand*{\fvtextcolor}[2]{\textcolor{#1}{#2}}

This should work:

\begin{Verbatim}[commandchars=&\[\]]
test&fvtextcolor[red][foo]test
\end{Verbatim}

Not with <>, I'm afraid: these two characters can't be used as delimiters in fancyvrb commandchars (I've already been bitten by this "feature").

[Tex/LaTex] LaTeX Verbatim Source Code Beside the Typeset Output

Here is an adaptation of Herbert's solution. The macro \DisplayAsLdots{} is used to wrap the contents of the source code which you want replaced with .... It uses \immediate\write18 to pre-processes the \jobname.vrb file through a sed script (thanks to David Carlisle and egreg) to produce the source code displayed on the right:

enter image description here

Notes:

This will only work on a Unix OS.
As Stephen Lehmke pointed out, there can not be any line breaks within the \DisplayAsLdots{} macro.
Since sed is greedy it will effectively gobble any other macros (and any content in between) that begin and end on the same line. So, code such as:
```
\DisplayAsLdots{foo} xyz \label{bar}
```
will be treated as if were (note where the parameter to \DisplayAsLdots ends):
```
\DisplayAsLdots{foo xyz \label{bar}}
```

Further Enhancements:

Adapt to work on non-unix operating systems (perhaps a pure LaTeX solution that does not require temporary files).
Use \ldots instead of three periods.
Enhance the regular expression for sed to allow for line breaks in \DisplayAsLdots, and terminate the replacement with the proper matching closing brace (to fix 3rd point in Notes section above).

Comment on this Presentation Style:

As mentioned in the comments, I really dislike this method of presentation. This stems from the fact that this documentation appears as if it is intended to illustrate how to use itemize lists to novice users -- My feeling is that anything that could possibly distract the reader should be minimized. In this example there are two issues that come to mind:

The use of the . . . (and the associated missing text).
The fact that there is an alignment between the input and the output.

With LaTeX there really is no such thing as a line by line comparison with the input and the output, so to show an example where things appear to be aligned will require additional work from the reader to comprehend.

I would rather see the full input text and output so I can see the correspondence between the input and the output.

Keep in mind that this is just personal opinion, others might prefer this style.

Code:

\documentclass{article}
\usepackage{enumitem}
\usepackage{blindtext}
\usepackage{fancyvrb}
\usepackage{listings}

\setlist[itemize]{leftmargin=*}%

\newcommand*{\DisplayAsLdots}[1]{#1}%

\newlength\CodeWidth
\makeatletter
\newenvironment{ShowCode}[2][]
  {\lstset{#1}\VerbatimEnvironment%
   \global\CodeWidth=#2%
   \begin{VerbatimOut}{\jobname.vrb}}
  {\end{VerbatimOut}\settowidth\@tempdima{\lstinputlisting{\jobname.vrb}}%
   \ReplaceDisplayedLdots%
   \noindent%
   \minipage[t]{\CodeWidth}\vspace{0pt}\input{\jobname.vrb}\endminipage\hfill%
   \minipage[t]{\dimexpr\@tempdima-2\fboxsep-2\fboxrule\relax}
     \vspace{0pt}\lstinputlisting{\jobname.vrb.new}\endminipage}

\newcommand{\ReplaceDisplayedLdots}{%
    \immediate\write18{%
          cat \jobname.vrb%
        | sed -e 's|\string\\DisplayAsLdots{.*}|...|'%
        > ./\jobname.vrb.new%
    }%
}%
\makeatother


\begin{document}
\blindtext

\begin{ShowCode}[language={[LaTeX]TeX},frame=single,columns=fixed,
   basicstyle=\small\ttfamily,breaklines,
   keywordstyle=\bfseries,
]{0.50\linewidth}
\begin{itemize}
\item Each list is \DisplayAsLdots{marked with a \emph{label}.  The labels in this itemized list are}  bullets.
\item List can be \DisplayAsLdots{nested within} one another.
\begin{enumerate}
   \item The item labels \DisplayAsLdots{in an enumerated list are numberals or} letters.
   \item A list should \DisplayAsLdots{have at least} two items.
\end{enumerate}
\LaTeX\ permits at least four levels \DisplayAsLdots{of nested lists, which is} more than enough.

\item Blank lines \DisplayAsLdots{before an item} have no effect.
\end{itemize}
\end{ShowCode}
\end{document}