-- Primer on representing non-printable characters in Lua code
function assert_equal(a, b)
  if a ~= b then
    error(a .. ' is not equal to ' .. b)
  end
end

-- Escape sequences in string use decimal character codes, i.e.
assert_equal('\97\98\99', 'abc')

-- Bytes in the string can be retrieved with string.byte(s, 0, -1)
local bytes = {string.byte('abc', 0, -1)} -- type(bytes) == 'table', #bytes == 3
assert_equal(table.concat(bytes, ', '), '97, 98, 99')

-- print(s) prints octal encoded escape sequences (WTF?)
print('\128') -- will print '\200'

-- To get the string which can be put back into source file you can
local eprint = function(s) print('\\' .. table.concat({string.byte(s, 0, -1)}, '\\')) end
eprint('abc') -- will print '\97\98\99'

-- Or to keep printable chars
    local eprint = function(s)
      local bytes = {}
      for i=1,#s do
        local byte = string.byte(s, i)
        if byte >= 32 and i <= 126 then
          byte = string.char(byte)
        else
          byte = '\\' .. tostring(byte)
        end
        table.insert(bytes, byte)
      end
      print(table.concat(bytes))
    end


-- Print string with non printable characters to be put in source code
-- "string with non printable".bytes.to_a.map {|i| i >= 32 && i <= 126 ? i.chr : "\\#{i}" }.join

-- String from Ruby to Lua
> '\\' + abc'.unpack('C*') * '\\' # => "\\97\\98\\99"

-- From Lua bytes to Ruby string
> [97, 98, 99].pack('c*')
"abc"