The File System
The Mac OS X file system is similar to other UNIX-based operating systems, but there are some significant differences in the file system structure and in case sensitivity. These differences are described in the sections that follow.
In this section:
File-System Structure and Visibility
Supported File-System Types
File-System Structure and Visibility
The file-system structure of Mac OS X is similar to a BSD-style system. A quick glance at hier should comfort you. When in doubt as to where to put things, you can put them where you would in a BSD-style system.There are a few directories that you might not recognize. These differences are described in more detail in “File System Organization.”
The default behavior of the Mac OS X Finder is to hide the directories that users normally would not be interested in, as well as invisible files, such as those preceded by a dot (.). This appearance is maintained by the Finder to promote simplicity in the user interface. As a developer, you might want to see the dot files and your complete directory layout. The /usr/bin/defaults tool allows you to override the default behavior of hiding invisible files. To show all of the files that the Finder ordinarily hides, type the following command in the shell:
defaults write com.apple.Finder AppleShowAllFiles true |
Then restart the Finder either by logging out and back in or by choosing Force Quit from the Apple Menu.
There are a couple of other simple ways to view the contents of hidden folders without modifying the default behavior of the Finder itself. You can use the /usr/bin/open command or the Finder Go to Folder command. With open you can open a directory in the Finder, hidden or not, from the shell. For example, open /usr/include opens the hidden folder in a new Finder window. If you are in the Finder and want to see the contents of an invisible folder hierarchy, choose Go to Folder from the Go menu, or just press command-~, and type in the pathname of your desired destination.
For information on how to lay out the directory structure of your completed Mac OS X applications, consult Apple Human Interface Guidelines and Mac OS X Technology Overview.
Supported File-System Types
Mac OS X supports Mac OS Extended (HFS+), the traditional Macintosh volume format, and the UNIX File System (UFS). HFS+ is recommended and is what most users have their system installed on. Some more server-centric installations have their system installed on UFS. If you develop on UFS, you should thoroughly test your code on HFS+ as well. Although the HFS+ file system preserves case, it is not case sensitive. This means that if you have two files whose names differ only by case, the HFS+ file system regards them as the same file. In designing your application, you should therefore not attempt to put two objects with names that differ only by case in the same directory—for example Makefile and makefile.
However, developing on HFS+ does not necessarily ensure that your application will work on UFS. It is far too easy to write code in which your program opens a file as org.mklinux.formattool.prefs one time and as org.MkLinux.formattool.prefs another time and gets completely different results.
Also, do not assume that a bug is unimportant simply because you have seen it only on UFS. Other file systems have similar properties, including potentially an NFS, SMB, or AFP share, particularly when those shares are being served by something other than a Mac. Thus, a bug that occurs on one file system will likely occur on others.
Last updated: 2008-04-08
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