.PLIST

Introduction

A property list is how macOS, iOS and their apps store settings and small amounts of structured data. App preferences, the Info.plist that describes every app bundle, and many system settings are property lists. The format came to Apple from NeXT.

A property list holds a tree of simple values: dictionaries, arrays, strings, numbers, booleans, dates and raw data. The same tree can be saved as readable XML or as a compact binary file, and Apple’s tools convert freely between the two.

Software

• Xcode, which has a property list editor (macOS)
• plutil, a command line tool built into macOS that checks and converts property lists
• PlistEdit Pro (macOS)
• ProperTree, a property list editor (Windows, macOS, Linux)

Structure

An XML property list has a <plist version="1.0"> root holding one value. Dictionaries are <dict> elements with alternating <key> and value elements, and the values are <string>, <integer>, <real>, <true/>, <false/>, <date>, <data> in base64, <array> and nested <dict>.

A binary property list starts with bplist00. The objects follow, each starting with a marker byte whose high four bits give its type and whose low four bits give its size. Arrays and dictionaries refer to their members by number. An offset table gives the position of every object, and a 32-byte trailer at the very end gives the sizes used, the number of objects, the top object and where the offset table starts.