eval-metadata.lua

local yaml_template = "---\nDUMMY: %s\n---"

function evaluate (str)
  local tag, value = str:match('^:(%a*):(.*)')
  if tag == 'lua' then
    return load(
      'return ' .. value,
      "evaluating " .. value
    )()
  elseif tag == 'json' then
    return pandoc.read(yaml_template:format(value)).meta['DUMMY']
  end
  return str
end

function Meta (meta)
  for key, value in pairs(meta) do
    if type(value) == 'string' then
      meta[key] = evaluate(value)
    end
  end
  return meta
end

Lua filter which evaluates specially marked metadata that has been passed through the command line. It allows to use either JSON or Lua.

Example:

pandoc --lua-filter=eval-metadata.lua --to=markdown -s \
    --metadata lua-test=':lua:{one="Hello",two={pandoc.Strong"World!"}}' \
    --metadata json-test=':json:["*emphasized*", "`code`"]' \
    <<< test

Result:

---
json-test:
- '*emphasised*'
- '`code`'
lua-test:
  one: Hello
  two: '**World**'
---

test