Asynchronous logging library for Lua
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Logging library for Lua 5.1/5.2

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Write to roll file and to console

local LOG = require "log".new(
  -- maximum log level

  -- Writer
  require 'log.writer.list'.new(               -- multi writers:
    require 'log.writer.console.color'.new(),  -- * console color
    require 'log.writer.file.roll'.new(        -- * roll files
      './logs',                                --   log dir
      'events.log',                            --   current log name
      10,                                      --   count files
      10*1024*1024                             --   max file size in bytes

  -- Formatter
  require "log.formatter.concat".new()

LOG.error("some", "error")

Write to file from separate thread

local LOG = require "log".new(
  require "log.writer.async.zmq".new(
    function() -- calls from separate thread/Lua state
      return require 'log.writer.file.by_day'.new(
        './logs', 'events.log', 5000

LOG.error("some error")

More complex example

local host = arg[1] or ''
local port = arg[2] or 514

-- this code run in separate thread.
local InitWriter = [[
  return require 'log.writer.list'.new(                  -- multi writers:
    require 'log.writer.console.color'.new(),            -- * console color
    require ''.new('%{zmq_cnn_host}'), -- * zmq pub socket
    require "log.writer.format".new(                     -- * syslog over udp
      require "log.logformat.syslog".new("user"),
      require ''.new('%{udp_cnn_host}', %{udp_cnn_port})

-- create async writer and run new work thread.
-- communicate with work thread using zmq library
local writer = require "log.writer.async.zmq".new(
  InitWriter:gsub('%%{(.-)}', {
    zmq_cnn_host = 'tcp://' .. host .. ':' .. port;
    udp_cnn_host = host;
    udp_cnn_port = port;

-- create new logger
local LOG = require"log".new(writer)

require "socket".sleep(0.5) -- net.zmq need time to connect

LOG.fatal("can not allocate memory")
LOG.error("file not found")
LOG.warning("cache server is not started")"new message is received")
LOG.notice("message has 2 file")

print("Press enter ...") io.flush()

Sendout logs to separate process/host

This example show how to send logs in 2 separate destination with 2 formats. Write to stdout as whell as to remote syslog server. In fact here no async on Lua side. Application write to network directly from main thread. But it is possible use one or more work threads that will do this.

-- Buld writer with 2 destinations
local writer = require "log.writer.list".new(
  require "log.writer.format".new(
    -- explicit set logformat to stdout writer
    require "log.logformat.default".new(), 
    require "log.writer.stdout".new()
  -- define network writer.
  -- This writer has no explicit format so it will
  -- use one defined for logger.
  require "".new('', 514)

local function SYSLOG_NEW(level, ...)
  return require "log".new(level, writer,
    require "log.formatter.mix".new(),
    require "log.logformat.syslog".new(...)

local SYSLOG = {
  -- Define first syslog logger with some settings
  KERN = SYSLOG_NEW('trace', 'kern'),
  -- Define second syslog logger with other settings
  USER = SYSLOG_NEW('trace', 'USER'),

SYSLOG.KERN.emerg ('emergency message')
SYSLOG.USER.alert ('alert message')






  • LuaLanes - This is experemental writer


  • ansicolors
  • or lua-conio
  • or cio (Windows only)