doi2url.lua

-- Time-stamp: <2024-04-20T21:07:41+0200 mpiotrow>

--[[ When converting from biblatex to bibtex, Pandoc only considers
   URL fields: DOIs get lost in the conversion (see
   <https://github.com/jgm/pandoc/blob/main/src/Text/Pandoc/Citeproc/BibTeX.hs>).

   This filter copies the values of DOI fields to URL fields, so that
   they are output to bibtex. ]]

function Pandoc(d)
   refs = pandoc.utils.references(d)

   local i, entry = next(refs, nil)

   while i do
      if refs[i].DOI then
         refs[i].URL = "https://doi.org/" .. refs[i].DOI
      end

      i, entry = next(refs, i) -- get next index
   end

   d.meta.references = refs
   return d
end

Usage:

pandoc -f biblatex -t bibtex -L doi2url.lua bibliography.bib

I’m using this filter in conjunction with getbib.lua to extract the references cited in a document from the main database (in biblatex format) into a BibTeX file, approximately like this:

pandoc -t bibtex -L getbib.lua -L doi2url.lua --bibliography=bibliography.bib -o references.bib *.md