Expansion of verbatim material

Question

I am passing a file name in the command line which contains underscores and would like to print the name of the file in the resulting PDF. So, need some expansion magic so that the output is:

The MWE produces:

In case it matters, the actual use case is with extract pages to incorporate the original file name in the extract PDF.

Code: MWE

\providecommand\FileName{A_B}
\documentclass{article}
\usepackage{verbdef}

\verbdef\MyVerb|\FileName|

\begin{document}
    \MyVerb\ (This should be ``\verb|A_B|", not ``\verb|\FileName|".)
\end{document}

Code: Actual Use Case

\providecommand*{\FileName}{A_B}%
\providecommand*{\PageRange}{2}% "3,67-70,80" for example (without the quotes)
\documentclass{article}
\usepackage{pdfpages}

\begin{document}
    \includepdf[pages={\PageRange},picturecommand={\FileName}]{"\FileName"}
\end{document}

Answer 1

\verb has no effect on tokens (even if you expanded \FileName), so you want something more like this

\def\FileName{A_B}
\documentclass{article}
\usepackage[T1]{fontenc}



\begin{document}
  \texttt{\detokenize\expandafter{\FileName}}
\end{document}