I have a shiny app with various chunks of text in markdown formatted files. In other contexts I would parameterise those files and use the m4 macro processor to do the substitutions.
The code would be something like markdown(read_file(pipe("m4 markdownfile.md")))
This needs m4 installed to work. Is it installed on shinyapps.io? Or perhaps there is another way of achieving the same goal ... parameterised files of text.