Set KDE/XDG file associations in bulk

set-file-association.rb

#!/usr/bin/env ruby

# A script to bulk change file associations.  Intended for KDE, but might work
# with other XDG conforming software.  Run it without arguments to see how to
# use it.  Created by me out of frustration, so the code just works ;)

require "inifile" # gem install inifile

ASSOC_FILE = "#{ENV['HOME']}/.config/mimeapps.list"
ASSOC_FILE_BAK = "#{ASSOC_FILE}.bak"
MIME_TYPES = File.readlines("/etc/mime.types").map{|line| line.split(/\s/).first}.reject(&:empty?)
APPLICATION_DIRS = %W[/usr/share/applications #{ENV['HOME']}.local/share/applications]

mime_type = ARGV[0]
program = ARGV[1]

if !mime_type || !program
  puts "#$0 - Bulk change file associations in KDE (and possibly others)"
  puts "Usage: #$0 <MIME-Type> <Program>"
  puts "  <Program>: The program to use (.desktop file)"
  puts "  <MIME-Type>: The MIME-Type to change. Examples:"
  puts "    video/mp4  Exactly video/mp4"
  puts "    video/     Match everything in the video group"
  puts "    /pdf       Match pdf in every group"
  puts
  puts "Changes to #{ASSOC_FILE} are stored at #{ASSOC_FILE_BAK}"
  puts "Directory files are stored in: #{APPLICATION_DIRS.join(', ')}"
  exit 0
end

program += ".desktop" unless program.end_with?('.desktop')
known = APPLICATION_DIRS.find{|path| File.exist? "#{path}/#{program}"}

if known.nil?
  puts "Can't find file #{program.inspect} in any of the following directories:"
  APPLICATION_DIRS.each{|path| puts "  #{path}"}
  exit 1
end

change = [ mime_type ]

if mime_type.end_with? '/'
  change = MIME_TYPES.select{|type| type.start_with? mime_type}
elsif mime_type.start_with? '/'
  change = MIME_TYPES.select{|type| type.end_with? mime_type}
end

#
change.each{|mime| puts "Changing #{mime} -> #{program}"}
mapping = change.map{|mime| [ mime.downcase, program ]}.to_h

ini = IniFile.load(ASSOC_FILE)
ini['Default Applications'].merge! mapping

#
puts "Writing backup to #{ASSOC_FILE_BAK}"
File.write ASSOC_FILE_BAK, File.read(ASSOC_FILE)

puts "Writing #{ASSOC_FILE}"
ini.write