How do I write the hashtag symbol # into an output file?

Question

I was successful before in writing the hashtag symbol # into an output file. please see the following MWE.

\documentclass{book}
\usepackage{newverbs}

\Verbdef\myHashtagSymbolOne{#}%
\newcommand*{\myWriteNewLine}{^^J}%
\newwrite\myOutputFileName%

\begin{document}
\edef\myHashtagSymbolTwo{\myHashtagSymbolOne}%
\edef\myHashtagSymbolThree{\detokenize\expandafter{\myHashtagSymbolTwo}}%

\immediate\openout\myOutputFileName=hashtag.tex%
\immediate\write\myOutputFileName%
{%
Here is my hashtag:%
\myWriteNewLine%
\myHashtagSymbolThree%
}%
\immediate\closeout\myOutputFileName%

\end{document}

I compiled using pdflatex with shellescape (MikTeX), which is working fine.

Note that the output file hashtag.tex used to contain exactly the following:

Here is my hashtag:

In the MWE, we can see that the goal is for \myHashtagSymbolThree to appear in the output file. We also notice that there are "intermediate" variables such as \myHashtagSymbolOne and \myHashtagSymbolTwo, which are necessary for my actual (long) program to run (and these variables serve other purposes in my program, but are no longer shown here.)

Now, I updated my MikTeX program just a few days ago. I also updated all packages, including the newverbs package. For one reason or another, when I compiled my program, the following now appears in the output file hashtag.tex:

Here is my hashtag:

\protect #

Suddenly, the unnecessary command \protect suddenly appeared. This appearance is unacceptable to me because my other programs which would use the output file are no longer functioning properly because of the appearance of \protect. To verify indeed that \protect is causing the problem, i removed/deleted it temporarily from the output file, and my other programs which use the output file are now working properly. This leads me to conclude that \protect should not be there. But I am at a loss why it suddenly appeared. What I wanted is for only the hashtag to appear (without the \protect).

Seeking kindly your help.

Answer 1

It works if I use TeX Live prior to the 2020 release, which uses newverbs version 1.4 or earlier; with TeX Live 2020 or 2021 I get newverbs version 1.6 that uses a different method for \Verbdef:

version 1.6

\newcommand*\Verbdef{%
    \@ifstar
        {\@Verbdef*}%
        {\@Verbdef{}}%
}
\def\@Verbdef#1#2{%
    \Collectverb#1{\DeclareRobustCommand#2}%
}

version 1.4

\newcommand*\Verbdef{%
    \@ifstar
        {\@Verbdef*}%
        {\@Verbdef{}}%
}
\def\@Verbdef#1#2{%
    \Collectverb#1{\def#2}%
}

Why did Martin choose for \DeclareRobustCommand I don' know: we can just see

% \changes{v1.6}{2021/01/06}{Changed \cs{Verbdef} to define robust commands.}

in the dtx file.

On the other hand, you can simply use \string#:

\immediate\write\myOutputFileName{%
  Here is my hashtag:\myWriteNewLine
  \string#
}
\immediate\closeout\myOutputFileName

A different method for collecting verbatim material and storing it in to a “named variable”, which doesn't suffer from the problem:

\documentclass{book}

\ExplSyntaxOn

\NewDocumentCommand{\xverbdef}{mv}
 {
  \tl_clear_new:c { l_xverbdef_#1_tl }
  \tl_set:cn  { l_xverbdef_#1_tl } { #2 }
 }
\NewExpandableDocumentCommand{\useverb}{sm}
 {
  \IfBooleanTF{#1}
   { \tl_use:c { l_xverbdef_#2_tl } }
   { \useverbp { #2 } }
 }
\NewDocumentCommand{\useverbp}{m}
 {
  \tl_use:c { l_xverbdef_#1_tl }
 }

\ExplSyntaxOff

\xverbdef{hash}{#}

\newcommand*{\myWriteNewLine}{^^J}

\newwrite\myOutputFileName

\begin{document}

\tableofcontents

\section{\useverb{hash}}

\immediate\openout\myOutputFileName=\jobname-out.tex
\immediate\write\myOutputFileName{%
  Here is my hashtag:\myWriteNewLine
  \useverb*{hash}%
}
\immediate\closeout\myOutputFileName

We can also use the character elsewhere \useverb{hash}

\end{document}

When you want to use the “raw” contents, do \useverb*{<name>}.

The printed output

The file written out

Here is my hashtag:
#

Answer 2

This will work. In fact, \myHashtagSymbolOne as well as \myHashtagSymbolTwo will also output a lone #.

\documentclass{book}
%\usepackage{newverbs}

\edef\myHashtagSymbolOne{\string#}%
\newcommand*{\myWriteNewLine}{^^J}%
\newwrite\myOutputFileName%

\begin{document}
\edef\myHashtagSymbolTwo{\myHashtagSymbolOne}%
\def\myHashtagSymbolThree{\myHashtagSymbolTwo}%

\immediate\openout\myOutputFileName=hashtag.tex%
\immediate\write\myOutputFileName%
{%
Here is my hashtag:%
\myWriteNewLine%
\myHashtagSymbolThree%
}%
\immediate\closeout\myOutputFileName%

\end{document}