From Mac Guides
Preferences for all applications and system software components are stored in a file in a Preferences folder, usually as plist files (plist is short for 'Property List'). They are used in all versions of Mac OS X.
The files contain a list of parameters that programs and system software use to define saved preferences. For example, the com.apple.dock.plist file contains a line enabling the dock to be hidden or permanently on. Sometimes a preferences files includes settings that cannot be edited using the programs 'Preferences' options and can only be modified using the Terminal or other editor.
Sometimes if a program is not behaving as it should, or refuses to run at all, deleting the preferences file can fix the problem. If a preferences file is damaged or corrupted a program may not be able to continue and by removing it the program will create a fresh file with the default settings. This will cause your preferences to be lost, which might include information like a serial number or other important settings. If you suspect a faulty preferences file, it is recommended that you make a back up of the file before deleting it.
There are three plist formats in use. All are functionally equivalent, and it is up to each program to decide which one it will use.
The OpenStep plist format is still occasionally seen under OS X. It uses a different bracket style for each data type, and may be altered with a regular text editor. See Old-Style ASCII Property Lists at Apple. The main advantage of this format is that it can be used with older OpenStep software.
With OS X came a move to a new XML plist format. It can also be modified with an editor such as TextEdit, and has the advantage that it can be read using existing non-Apple libraries. See XML Property Lists at Apple for details.
Starting with Mac OS X 10.2 (Jaguar), and seen frequently in 10.4 (Tiger), there is also a binary plist format. While it cannot easily be manipulated with a plain text editor, it is useful in programs that need to retain large amounts of data.
Editing Plist files
To make changes in plist files, it is recommended to use one of the following:
- In Terminal using the defaults command.
- The Property List Editor application that is included with the Mac OS X Developer Tools.