🚀 go-pugleaf

I am trying to write a tex macro that needs to print a
file name as part of what it does.  The macro does not
work if the file name has an underscore character in it,
since it interprets the underscore as the subscript
character and starts inserting $ signs.

The crux of what I am trying to do is:

\def\foo#1{ {\tt #1} }

\foo{file_name.ext}

I tried defining foo as follows:

\def\foo#1{ {\catcode`_=12 {\tt #1} } }

but that does not work either.  I tried many different
variations without any success.  It appears that I have
to do the catcode stuff when I invoke foo:

{\catcode`_=12 \foo{file_name.ext} }

Is there a way of avoiding this and doing everything
inside the macro?

Thanks,
mtr