Script that gets the path to your built product from an Xcode workspace no matter your build location (Derived Data or Legacy Build Directory)

xcode_build_settings.rb

#
# Usage: 
#  
#    app_path = product_path :workspace => "MyProject.xcworkspace",
#                            :scheme => "MyProjectScheme",
#                            :configuration => "Debug",
#                            :sdk => "iphonesimulator"
#
#    puts app_path //=> /Users/yourusername/Library/Developer/Xcode/DerivedData/MyProject-bltlcokzhdicjggqmcrwibpdgdcp/Build/Products/Debug-iphonesimulator/MyProject.app
#

def build_settings options = { :workspace => nil, :scheme => nil, :configuration => nil, :sdk => nil }
    build_output = `xcodebuild -workspace #{options[ :workspace ]} -scheme #{options[ :scheme ]} -configuration #{options[ :configuration ]} -sdk #{options[ :sdk ]} -showBuildSettings`
    Hash[build_output.split(/\r?\n/).collect { |setting|
        setting.split(' = ', 2).collect &:strip 
    }.reject { |setting| 
        setting.length != 2 || setting[0] == "" 
    }]
end

def product_path options = { :workspace => nil, :scheme => nil, :configuration => nil, :sdk => nil } 
    settings = build_settings options
    target_build_directory = settings[ "TARGET_BUILD_DIR" ]
    executable_file_directory = settings[ "EXECUTABLE_FOLDER_PATH" ]
    File.join(target_build_directory, executable_file_directory)
end

Seems like you could further simplify this code by using split instead of a regex when building your hash.

build_settings.collect do |setting|
  pair = setting.split(' = ', 2).collect &:strip
end

This was typed on an iPad, so it probably contains errors.