macOS Bundles

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Basic Information

Bundles in macOS serve as containers for a variety of resources including applications, libraries, and other necessary files, making them appear as single objects in Finder, such as the familiar *.app files. The most commonly encountered bundle is the .app bundle, though other types like .framework, .systemextension, and .kext are also prevalent.

Essential Components of a Bundle

Within a bundle, particularly within the <application>.app/Contents/ directory, a variety of important resources are housed:

_CodeSignature: This directory stores code-signing details vital for verifying the integrity of the application. You can inspect the code-signing information using commands like: %%%bash openssl dgst -binary -sha1 /Applications/Safari.app/Contents/Resources/Assets.car | openssl base64 %%%
MacOS: Contains the executable binary of the application that runs upon user interaction.
Resources: A repository for the application's user interface components including images, documents, and interface descriptions (nib/xib files).
Info.plist: Acts as the application's main configuration file, crucial for the system to recognize and interact with the application appropriately.

Important Keys in Info.plist

The Info.plist file is a cornerstone for application configuration, containing keys such as:

CFBundleExecutable: Specifies the name of the main executable file located in the Contents/MacOS directory.
CFBundleIdentifier: Provides a global identifier for the application, used extensively by macOS for application management.
LSMinimumSystemVersion: Indicates the minimum version of macOS required for the application to run.

Exploring Bundles

To explore the contents of a bundle, such as Safari.app, the following command can be used: bash ls -lR /Applications/Safari.app/Contents

This exploration reveals directories like _CodeSignature, MacOS, Resources, and files like Info.plist, each serving a unique purpose from securing the application to defining its user interface and operational parameters.

Additional Bundle Directories

Beyond the common directories, bundles may also include:

Frameworks: Contains bundled frameworks used by the application. Frameworks are like dylibs with extra resources.
PlugIns: A directory for plug-ins and extensions that enhance the application's capabilities.
XPCServices: Holds XPC services used by the application for out-of-process communication.

This structure ensures that all necessary components are encapsulated within the bundle, facilitating a modular and secure application environment.

For more detailed information on Info.plist keys and their meanings, the Apple developer documentation provides extensive resources: Apple Info.plist Key Reference.