Returns the definition of given word via Dictionary Services of macOS. (Install Ruby-FFI in advance)

macOSDict.rb

# -*- coding: utf-8 -*-
# Usage : $ macOSDict.rb [word_to_look_up]
require 'ffi'

module MacOSDict

  extend FFI::Library

  # /System/Library/Frameworks/CoreFoundation.framework/Headers/CFBase.h
  class CFRange < FFI::Struct
    layout :location, :int64,
           :length, :int64
  end

  KCFStringEncodingUTF8 = 0x08000100

  APIEntry = Struct.new( :api_name, :api_args, :api_retval )

  def self.load_lib(output_error = true)
    libpath = [
      "/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation",
      "/System/Library/Frameworks/CoreServices.framework/Frameworks/DictionaryServices.framework/DictionaryServices",
    ]
    ffi_lib(libpath[0])
    ffi_lib(libpath[1])
    @@api_signature = [
      APIEntry.new( :CFStringGetCStringPtr, [:pointer, :uint32], :pointer ),
      APIEntry.new( :CFStringCreateWithCString, [:pointer, :pointer, :uint32], :pointer ),
      APIEntry.new( :CFStringGetLength, [:pointer], :int64 ),
      APIEntry.new( :CFStringGetBytes, [:pointer], :int64 ),
      APIEntry.new( :CFStringGetCharacterAtIndex, [:pointer, :int64], :uint16 ),
      APIEntry.new( :CFStringGetCString, [:pointer, :pointer, :int64, :uint32], :uint8 ),
      APIEntry.new( :CFStringGetBytes, [:pointer, CFRange.by_value, :uint32, :uint8, :uint8, :pointer, :int64, :pointer], :int64 ),
      APIEntry.new( :DCSGetTermRangeInString, [:pointer, :pointer, :int64], CFRange.by_value ),
      APIEntry.new( :DCSCopyTextDefinition, [:pointer, :pointer, CFRange.by_value], :pointer ),
    ]

    @@api_signature.each do |sig|
      begin
        attach_function( sig.api_name, sig.api_args, sig.api_retval )
      rescue FFI::NotFoundError
        $stderr.puts("[Warning] Failed to import #{sig}.") if output_error
      end
    end

  end

end

include MacOSDict

if __FILE__ == $0

  MacOSDict.load_lib()

  query = ARGV[0]
  term = CFStringCreateWithCString(nil, query, KCFStringEncodingUTF8)
  term_range = DCSGetTermRangeInString(nil, term, 0)
  def_text = DCSCopyTextDefinition(nil, term, term_range)
  if def_text.null? == false
    def_range = CFRange.new
    def_range[:location] = 0
    def_range[:length] = CFStringGetLength(def_text)

    usedBufLen = ' ' * 8
    CFStringGetBytes(def_text, def_range, KCFStringEncodingUTF8, 0, 1, nil, 0, usedBufLen)

    result = ' ' * (usedBufLen.unpack("L")[0] + 1)
    CFStringGetCString(def_text, result, result.length, KCFStringEncodingUTF8)
    puts result
  end

end

# Reference:
# /System/Library/Frameworks/CoreFoundation.framework/Headers/
# - CFBase.h
# - CFString.h
# /System/Library/Frameworks/CoreServices.framework/Frameworks/DictionaryServices.framework/Headers
# - DictionaryServices.h