a node based event driven real time logfile parser
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nolog.js ... a node.js based real time event driven log file watcher

nolog lets you watch (log)files in real time and matches patterns (regular expressions, functions, booleans) to events.

** New: now an npm package **


  npm install nolog


  var $n = require("nolog");
  //or if you don't use npm
  //var $n = require("/path/to/nolog/nolog.js");

watch a file

  //returns a NologEventEmitter
  var log = $n("/path/to/the/logfile.log");

alternativly to $n(path) one can also write $n.watch(path)

you can either watch a file (just pass a "path/to/file-string") or any readableStream (http, https, ...) see http://nodejs.org/docs/v0.4.6/api/streams.html#readable_Stream

note: to test the included examples localy you might want to funnel your webservers logfiles to a local test.log

cd /path/to/nolog/
ssh server.example.com sudo tail -f /var/log/nginx/example.com_access.log > test.log

shout (throw an event) if a single logfile line matches an reguar expression

  //NologEventEmitter.watch(eventname, pattern)
  log.shoutIf('googlebot', /Googlebot/i );
  log.shoutIf('chrome', "Chrome" );

the pattern argument can either be a regular expression or a simple string ( means .*+?|()[]{}\ will be treated as 'normal' characters)

shoutIfNot is the same (but opposite) of shoutIf - shoutIfNot throws an event if the pattern did not lead to a successfull match.

  //NologEventEmitter.shoutIfNot(eventname, pattern)
  log.shoutIfNot('allNotGetRequests', "GET" );

shoutIf and shotIfNot start so called shout-jobs.

si and sin are shortcuts for shoutIf and shoutIfNot

assign an event handler

  //NologEventEmitter.on(eventname, callback)
  log.on('googlebot', function(data){ console.log("a Googlebot");});

on assigns an event handler to the NologEventEmitter listening for the eventname.

shoutIf and shoutIfNot assigned events return an RegExp return array https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/RegExp/exec#Description that's an array with a special index and input value.

as there was nothing found at shoutIfNot the index value is null, the first value of the array is also null. input is the parsed log line.

for other standard methods of NologEventEmitter see EventEmitter in the offical Node.js documentation http://nodejs.org/docs/v0.4.5/api/events.html#events.EventEmitter

kill a shoutIf or shoutIfNot job


no more googlebot events will be thrown. the shout-job with the name eventname gets killed.

unwatch a file


unwatch kills all shout-jobs (no more events get thrown) and stops the background task watching the specific file.

killAll is a synonym for unwatch

if you kill the last last shout-job of a watched file, the file is automatically unwatched. said that, the NologEventEmitter object is still valid, if you add a new shout-job, the file is automatically re-watched. (think: magic)


shout is fluffy shortcut for shoutIf

  log.shout('googlebot'); // == log.shoutIf('googlebot', /googlebot/i );

basically it shout throws an event with the name eventname if a case-iNsEnSeTiVE match for eventname was found.


  • all public methods support chaining (i.e.$n('access.log').s('bot').on('bot', function(d){ ... });

  • nolog.enableDebug(true) - turns on some debug output via console.log

  • NologEventEmitter.follow enables real time updates, default true

  • NologEventEmitter.wholefile parses the whole file from the beginning, default false (note: handle with care, can fire millions of events at once, not suitable for browser clients applications)

  • NologEventEmitter.setEncoding(encoding) - per default every file is parsed as 'utf8'

  • NologEventEmitter.jobs array that holds the jobs of the currently watched file

  • NologEventEmitter.fileErrorCallback(error) a method that gets called if something goes seriously wrong while watching a file, per default it throws an error.

the NologEventEmitter attributs and methods can be also passed as an object via the watch method.

  var log = $n("/path/to/the/logfile.log", {wholefile:true; follow:false});
  var log = $n.watch("/path/to/the/logfile.log", {wholefile:true; follow:false});



  log.shoutIf('bot', /bot/i, true );

additonally to the success event 'bot' another event is thrown, namely '!bot' if the pattern was not matched. this means, for evey parsed logline an event -either eventname or !eventname - is thrown.

this is not the same as shoutIfNot - shoutIfNot throws a success match, if something was not matched. as a matter of fact, shoutIfNot also supports enableNotEvent

  log.shoutIfNot('human', /bot/i, true );

if the logline does not match the '/bot/i' the event 'human' is thrown. if the logline matches the event '!human' is thrown. (note: notEvents are less confusing when used with shoutIf)

boolean patterns

si and sin (and their longer worded aliases shoutIf and shoutIfNot) also support booleans patterns.

  //get every line
  log.si('line', true).on('line', function(data){ ... });

the data value will always be a RegExp return array.

function callback patterns

si and sin (searchIf and searchIfNot) can also handle function patterns.

  //NologEventEmitter.searchIf(eventname, function-pattern). ...
  log.si('uniqueip', function(line){ ... }).on('uniqueip', function(returnvalue){ ... });

the return value of the function pattern gets returned to the event callback.

note: function patterns do not make too much sense with sin or notEvents, as the return value will always be a falsy value.


  • readable streams support (done)

  • make encoding editable, default utf8 (done)

  • add an exitcallback (open)

  • add before and after (every line) hooks (open)