I use this script to find bibliographical @references cited in my markdown files (using the Pandoc syntax) that happen to be absent from the bibliography file.

find_missing_references.rb

#!/usr/bin/env ruby
# frozen_string_literal: false

# I use this script to find bibliographical @references (using the Pandoc syntax) cited in my markdown files
# that happen to be absent in the bibliography file.

# Pandoc syntax: [@Ref] → (Author + Year) / [-@Ref] → (Year)

Encoding.default_external = Encoding::UTF_8

path = '/path/to/markdown/file.md'
bib_file = '/path/to/bib/file.bib'

md_input = File.open(path, 'r').read.split(/\n/)
bib = File.open(bib_file, 'r').read

found_references = []
missing_refs = []

md_input.each do |line|
    found_references.push(line.scan(/(?<!\\|\w|\+|\*|{|-|!)-*@(?!})(?!tbl)(?!fig)(?!sec)(?!eq)(\b.+?\b)/)) unless line.empty? || line.nil?
end

references = found_references.flatten.sort.uniq

references.each do |ref|
  found_item = bib.scan(ref).flatten[0]
  if found_item.nil?
    missing_refs.push(ref)
  end
end

puts "Missing references: " + missing_refs.join(', ')