My simple ID3v2 tag editor

id3editor.rb

#!/usr/bin/ruby

require 'rubygems'
require 'mp3info'
require 'readline'

TAGS = {
   "AENC" => "Audio encryption",
   "APIC" => "Attached picture",
   "COMM" => "Comments",
   "COMR" => "Commercial frame",
   "ENCR" => "Encryption method registration",
   "EQUA" => "Equalization",
   "ETCO" => "Event timing codes",
   "GEOB" => "General encapsulated object",
   "GRID" => "Group identification registration",
   "IPLS" => "Involved people list",
   "LINK" => "Linked information",
   "MCDI" => "Music CD identifier",
   "MLLT" => "MPEG location lookup table",
   "OWNE" => "Ownership frame",
   "PRIV" => "Private frame",
   "PCNT" => "Play counter",
   "POPM" => "Popularimeter",
   "POSS" => "Position synchronisation frame",
   "RBUF" => "Recommended buffer size",
   "RVAD" => "Relative volume adjustment",
   "RVRB" => "Reverb",
   "SYLT" => "Synchronized lyric/text",
   "SYTC" => "Synchronized tempo codes",
   "TALB" => "Album/Movie/Show title",
   "TBPM" => "BPM (beats per minute)",
   "TCOM" => "Composer",
   "TCON" => "Content type",
   "TCOP" => "Copyright message",
   "TDAT" => "Date",
   "TDLY" => "Playlist delay",
   "TENC" => "Encoded by",
   "TEXT" => "Lyricist/Text writer",
   "TFLT" => "File type",
   "TIME" => "Time",
   "TIT1" => "Content group description",
   "TIT2" => "Title/songname/content description",
   "TIT3" => "Subtitle/Description refinement",
   "TKEY" => "Initial key",
   "TLAN" => "Language(s)",
   "TLEN" => "Length",
   "TMED" => "Media type",
   "TOAL" => "Original album/movie/show title",
   "TOFN" => "Original filename",
   "TOLY" => "Original lyricist(s)/text writer(s)",
   "TOPE" => "Original artist(s)/performer(s)",
   "TORY" => "Original release year",
   "TOWN" => "File owner/licensee",
   "TPE1" => "Lead performer(s)/Soloist(s)",
   "TPE2" => "Band/orchestra/accompaniment",
   "TPE3" => "Conductor/performer refinement",
   "TPE4" => "Interpreted, remixed, or otherwise modified by",
   "TPOS" => "Part of a set",
   "TPUB" => "Publisher",
   "TRCK" => "Track number/Position in set",
   "TRDA" => "Recording dates",
   "TRSN" => "Internet radio station name",
   "TRSO" => "Internet radio station owner",
   "TSIZ" => "Size",
   "TSRC" => "ISRC (international standard recording code)",
   "TSSE" => "Software/Hardware and settings used for encoding",
   "TYER" => "Year",
   "TXXX" => "User defined text information frame",
   "UFID" => "Unique file identifier",
   "USER" => "Terms of use",
   "USLT" => "Unsychronized lyric/text transcription",
   "WCOM" => "Commercial information",
   "WCOP" => "Copyright/Legal information",
   "WOAF" => "Official audio file webpage",
   "WOAR" => "Official artist/performer webpage",
   "WOAS" => "Official audio source webpage",
   "WORS" => "Official internet radio station homepage",
   "WPAY" => "Payment",
   "WPUB" => "Publishers official webpage",
   "WXXX" => "User defined URL link frame"
}

mp3 = ARGV[0]

def help
   puts <<HELP
id3editor

Commands : 
   - info : display file info
   - list : list availables ID3v2 tags
   - quit : save and quit
   - help : display this page

Usage :

   To change a tag value, use :

   > TAG = value

   where TAG is a valid ID3v2 tag

   Most common tags : TABL, TPE1, TIT2

Licence :

   DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
   Version 2, December 2004 

   Copyright (C) 2011 Grégoire Lejeune <gregoire.lejeune@free.fr>

   Everyone is permitted to copy and distribute verbatim or modified 
   copies of this license document, and changing it is allowed as long 
   as the name is changed. 

   DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 

   0. You just DO WHAT THE FUCK YOU WANT TO. 

   This program is free software. It comes without any warranty, to
   the extent permitted by applicable law. You can redistribute it
   and/or modify it under the terms of the Do What The Fuck You Want
   To Public License, Version 2, as published by Sam Hocevar. See
   http://sam.zoy.org/wtfpl/COPYING for more details.
HELP
end

def show(tag2)
   tag2.each do |k, v|
      puts "(#{k}) #{TAGS[k]} : #{v}"
   end
end

Mp3Info.open(mp3) do |info|
   help

   while cmd = Readline.readline('> ', true)
      cmd.chomp!
      cmd.strip!
      break if cmd =~ /quit/

      if cmd =~ /list/
         TAGS.each do |k, v|
            puts "#{k} : #{v}"
         end
      elsif cmd =~ /info/
         show(info.tag2)
      elsif cmd =~ /help/
         help
      else
         data = nil
         if r = /^([^\=]*)=(.*$)/.match(cmd)
            cmd = r[1].strip
            data = r[2].strip
         end
         if TAGS.keys.include?(cmd)
            unless data.nil?
               info.tag2[cmd] = data
            end
            puts "#{TAGS[cmd]} : #{info.tag2[cmd]}"
         else
            puts "Unknow tag #{cmd}"
         end
      end
   end
end