Plists and plutil
Configuration files are a problem for both operating systems and applications. Where do you keep them, how are they structured?
Traditional Unix systems use text files with wildly varying internal structures, and Windows used either binary data or text files. Windows now uses
a central registry that is accessed by a "regedit" application, and most
Unix systems still use text files.
The benefit of using a simple text format for configuration files is
obvious: Assuming you know what file to edit, there's nothing new to learn;
you use a text editor. There are no indexes or internal pointers to get
out of whack. The text file may have specific structural requirements,
but the structure is often obvious through visual inspection. From
an application point of view, reading text files may be slower,
but realistically that is almost insignificant. There is also the annoyance
of converting any required binary values to and from text, but again, that shouldn't be anything that really slows down the process.
However, the ease of editing can be seen as a disadvantage also: if a
proprietary tool is used, that tool can impose
consistency checks and possibly avoid the introduction of incorrect
What's all this got to do with Mac OS X? As we know, OS X is Unix, but
Apple has taken a different approach by using XML property
lists for most configuration data. Using XML provides a consistent data
format that is easily hand or program edited.
XML property lists are text, but text with definite structure.
Every piece of information stored in an XML file follows the same
XML syntax, which means that its possible to write programs to
check the validity of these files. So, if an property list
file gets corrupted, we can identify that problem by checking
for proper XML syntax. The tool that does that is "plutil"
There's nothing difficult about this tool. Open up Terminal, and
sudo plutil -s ~//Library/Preferences/*.plist /Library/Preferences/*plist
I've read that plutil can think there's a problem where there is
none, though I've never experienced that. It's not a bad idea to
keep safe copies of known good plist files where you can get at them
quickly if necessary.
Plists can be stored in binary format; plutil can convert such
files back to text for manual inspection. See the man page.
If you have extreme fear of the command line, "Preferential
Treatment" (http://www.versiontracker.com/dyn/moreinfo/macosx/22790) wraps plutil in a GUI interface for you.
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