Macro parameter character in \input file

I would like to include some paragraphs from external .tex files in my document, very similar to what \lipsum does. As far as I understood it until now is using \input equivalent to directly typing text and commands.

However, when running the MWE below

\begin{filecontents}{myTextFile.tex}
\ifthenelse{#2=1}{first paragraph}{}
\ifthenelse{#2=2}{second paragraph}{}
\end{filecontents}

\documentclass{report}
\usepackage{ifthen}
\newcommand\myParagraphs[2]{\input{#1}}

\begin{document}
\myParagraphs{myTextFile.tex}{2}
\end{document}


I get the error message

You can't use macro parameter character #' in horizontal mode.

Thus, '#2' is not known in myTextFile.tex. How can I make #2 known there, or is there an easier way to define \myParagraphs{<file>}{<paragraph no>}

You can't do like that. The definition of \myParagraphs doesn't use #2; so

\myParagraphs{myTextFile.tex}{2}


becomes

\input{myTextFile}


and so TeX reads your file, where #2 is illegal. Here's a way: define a temporary macro to expand to the value of #2:

\begin{filecontents}{myTextFile.tex}
\ifthenelse{\second=1}{first paragraph}{}
\ifthenelse{\second=2}{second paragraph}{}
\end{filecontents}

\documentclass{report}
\usepackage{ifthen}
\newcommand\myParagraphs[2]{\def\second{#2}\input{#1}}

\begin{document}
\myParagraphs{myTextFile.tex}{2}
\end{document}


AFAIK you cannot collect stuff that way. You need to store each paragraph in a macro with a name that can then be chosen via an option. That is how lipsum etc. works.

It might be an idea to use etoolbox and its \csdef macro to build the macros and \csuse` to execute them.