shellescape macro nested in another macro

Question

How do I use a shellescape (| echo "stuff") macro as another macros input if there are "bad" characters like _ contained.

I will use my full example as reference.

The idea is to replace \lstinputlisting{|\string"git archive --remote=ssh://git@server/repo.git VERSION path/to/file 2>/dev/null | tar --extract --file - --to-stdout\string"}

with a macro like this

% set these so they can later be redefined
\providecommand{\GitRemote}{}
\providecommand{\GitIdentifier}{master}

\providecommand{\GitCheckout}[2][\GitIdentifier]{%
% #1 being the version/branch
% #2 being the file
| \string"git archive --remote=\GitRemote #1 \detokenize{#2} 2>/dev/null | tar --extract --file - --to-stdout \string"%
}

with usage \lstinputlisting{\GitCheckout{path_to_file.py}}

MWE:

\documentclass{article}
\usepackage{listings}
\providecommand{\GitRemote}{}
\providecommand{\GitIdentifier}{master}
\providecommand{\GitCheckout}[2][\GitIdentifier]{%
% #1 being the version/branch
% #2 being the file
| \string"git archive --remote=\GitRemote #1 \detokenize{#2} 2>/dev/null | tar --extract --file - --to-stdout \string"%
}
\begin{document}
renewcommand{\GitRemote}{ssh://git@trac.sagemath.org/sage.git}
\lstinputlisting{\GitCheckout{src/sage/coding/goppa.py}}
\end{document}

but i keep getting errors like this

mwe.tex|10 error| Use of \\GitCheckout doesn't match its definition.

so it seems there is some escaping going on (\ to \\)

Answer 1

There were multiple problems in this code:

We do not want to escape any character, if used as an input and, as @David Carlisle mentioned, the input for lsinputlistings needs to be expanded. The optional structure is, as @egreg mentioned, better delegated to xparse. For getting an optional command I used the DeclareExpandableDocumentCommand from (i think) here.

Combining these facts we get a function definition of the macro and prequisites as follows:

% https://tex.stackexchange.com/questions/501640/shellescape-macro-nested-in-another-macro?noredirect=1#comment1266953_501640
\usepackage{xparse}

% this is set as fallback
\NewDocumentCommand{\GitRemote}{}{}
\NewDocumentCommand{\GitIdentifier}{}{master}


\NewExpandableDocumentCommand{\GitCheckout} {O{\GitIdentifier} O{\GitRemote} m} {%
|"git archive --remote=#2 #1 #3 2>/dev/null | tar --extract --file - --to-stdout"
}