A file is a basic unit of filesystem currency in any modern operating
system. The following sections discusses some of the file
types you’ll find in Mac OS X.
Mac OS X’s Application-to-Document Map
The system determines a
document’s kind in one of two
ways. First it sees if the document has an attribute
fork, a data attachment possessed by documents created by
Classic and Carbon applications that provides information about the
document’s type (among other things). If the file
lacks a attribute fork, it looks to the document’s
filename extension; Mac OS X maintains a system- wide map between
these extensions and recognized document types.
The system’s map that binds particular filename
extensions to certain Aqua applications is made from two sorts of
files. Each application’s Info.plist
file (see Chapter 22) can define the
filename extensions its documents use. For example, Terminal
application files have the extension .term, and
it says as much in its Info file (located, for the curious, at
If only one application lays claim to a particular file extension (as
is the case with .term, at least in a fresh Mac
OS X installation), the system will recognize a binding between that
application and all files with that extension; double-clicking these
documents in the Finder will open them through that application.
These claims, however, may be overruled by the contents of another
com.apple.LaunchServices.plist, which is another ...
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