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A Ruby library for examining and modifying Mach-O files.

What is a Mach-O file?

The Mach-O file format is used by OS X and iOS (among others) as a general purpose binary format for object files, executables, dynamic libraries, and so forth.


Full documentation is available on RubyDoc.

A quick example of what ruby-macho can do:

require 'macho'

file ="/path/to/my/binary")

# get the file's type (MH_OBJECT, MH_DYLIB, MH_EXECUTE, etc)
file.filetype # => "MH_EXECUTE"

# get all load commands in the file and print their offsets:
file.load_commands.each do |lc|
    puts "#{lc}: offset #{lc.offset}, size: #{lc.cmdsize}"

# access a specific load command
lc_vers = file['LC_VERSION_MIN_MACOSX'].first
puts lc_vers.version_string # => "10.10.0"

What works?

  • Reading data from x86/x86_64 Mach-O files
  • Changing the IDs of Mach-O dylibs
  • Changing install names in Mach-O files

What might work?

  • Reading some data from PPC Mach-O files.
  • Reading data from "Fat" files.

What doesn't work yet?

  • Reading data from any other architecure's Mach-O files (probably).
  • Changing anything in "Fat" files (at least not correctly).

What needs to be done?

  • Documentation.
  • Rpath modification.
  • Many, many things.


  • lib/macho/cstruct.rb was taken from Sami Samhuri's compiler repository. (No license provided).
  • Constants in lib/macho/macho.rb were taken from Apple, Inc's loader.h in cctools/include/mach-o. (Apple Public Source License 2.0).


ruby-macho is licensed under the MIT License.

For the exact terms, see the license file.