A library for parsing IRC lines.

$ opm get jprjr/irc-parser



An IRC parser in LPEG, with a pure-Lua fallback. Supports IRCv3 message tags.


    local parser = require('irc-parser').new()
    local line = '@message-id=12345;some-content=hello\\sthere;empty-str=;empty :nick! PRIVMSG #a-room ::-) Hi there!'
    local parsed, pos = parser(line)
      parsed is a table:
        tags = {
          empty = false,
          ["empty-str"] = false,
          ["message-id"] = "12345",
          ["some-content"] = "hello there"
        source = {
          host = "",
          nick = "nick",
          user = "user"
        command = "PRIVMSG",
        params = { "#a-room", ":-) Hi there!" },
      pos is the length of the string + 1, so in this case 115



Available on luarocks:

    luarocks install irc-parser


Available on OPM

    opm install jprjr/irc-parser


By default, you can require('irc-parser'), and it will automatically choose an appropriate backend.

It will first try to load the LPEG-based backend, and fall back to the pure-Lua backend if LPEG is not available.

You can force a specific backend by requiring it: require('irc-parser.fallback') for the Lua fallback, and require('irc-parser.lpeg') for the LPEG version.


You can then instantiate a parser with .new([mode],[opts]) (or just call the returned module directly like parser = require('irc-parser')([mode],[opts]).

The mode argument is optional. If not specified, the parser will be in LOOSE mode.

There's three different modes available:

  • LOOSE - aims to be broadly-compatible.

  • STRICT - follows the IRC RFCs as closely as possible.

  • TWITCH - essentially STRICT with a few modifications for Twitch's IRC interface.

The default LOOSE mode should work on most IRC servers, including Twitch. In my testing, it's also the fastest (since it performs less validations than any other mode).

You can specify which mode you'd like in a few ways:

    -- these are all equivalent:
    -- use a string name
    local strict_parser = require('irc-parser')('strict')
    local strict_parser = require('irc-parser')('STRICT')
    -- use an enum
    local mod = require('irc-parser')
    local strict_parser =

The opts argument is a table of options to fine-tune handling of empty and missing tag values. By default, empty and missing tags are converted to the boolean false.

If you'd prefer a different value for either empty or missing tags (example, say you want empty tags to remain empty strings), you can:

    local parser = require('irc-parser')('loose', {
      empty_tag_replacement = '',

And now empty tags will be returned as empty strings, missing tags will remain as false.

You can also specify that you'd like empty and missing strings to be removed entirely:

    local parser = require('irc-parser')('loose', {
      remove_empty_tags = true,
      remove_missing_tags = true,


The parser exposes a single method, parser:parse(str, [pos]). The parser itself can also be called as a function, parser(str, [pos]).

It accepts a string argument, the string argument can be terminated with a newline character, or a carriage return and newline, or nothing. It also accepts an optional position argument, this should be a number indicating where to start parsing.

If successful, it will return a parsed table, and the position for the next parse (essentially the length of the line + 1). This position argument is so you can have a string with multiple lines.

If not successful, it returns nil.

Here's an example of looping through a block of data using the position argument and return value.

The returned table will have the following keys:

  • tags - a table of tag values, or nil if no tags were attached to the message.

  • source - a table representing the message source with the keys host, nick, and/or user. source will be nil if there was no source on the message.

  • command - an IRC command (ie, PRIVMSG, 001, etc).

  • params - an array-like table of parameters, or nil if there were no parameters.

    local parser = require('irc-parser').new()
    -- we'll say that "raw.txt" is a raw IRC log file with multiple lines
    local rawfile ='raw.txt','rb')
    local rawdata = rawfile:read('*a')
    local parsed
    local pos = 1
    while pos < #rawdata do
      parsed, pos = parser:parse(rawdata,pos)
      if not parsed then
      -- do something with parsed


MIT (see file LICENSE).


John Regan