function parse(pattern)
  pattern = pattern
    :gsub("<quoted>", "([^\"]*)")
    :gsub("<quoted2>", "([^\"]*)")
    :gsub("<rest>", "(.*)")
  return input:match("^"..pattern.."$")
end

if input == "" then return "" end

cmdpattern = 'replace "<quoted>" with "<quoted2>" in this text: <rest>'
pattern, replacement, text = parse(cmdpattern)
if pattern then
  return text:gsub(pattern, replacement) -- simplest solution - no escaping for now
else
  return("Error. Syntax: "..cmdpattern) -- for now return instead of error because error doesn't seem to work that great yet
end