Follow-up to my previous post about receipt files. Again, this is Mac-centric.
WHAT IS AN APPLICATION BUNDLE?
"Application bundle" is Cocoa developer terminology for an application as it exists in the file system of your computer. The application consists of a number of files organized in a directory. The directory has special attributes and has a specific subdirectory structure.
WHERE IS THIS DIRECTORY? ALL I SEE IS THE APPLICATION FILE.
You only think you see a regular file. When you see an application icon in the Finder, such as the Safari icon, it looks like any other file icon. However, the Finder is telling at least two and possibly three lies about the application.
LIE #1: HIDING THE .app EXTENSION
On the file system, the name of the application is not actually "Safari" (for example) but "Safari.app", with a ".app" extension.
You can see all the .app extensions in Terminal:
ls /Applications
You can also see an application's filename in the Finder by selecting the application icon and doing a Get Info. You'll see the ".app" extension. Alternatively, if you go to Preferences > Advanced and turn on "Show all filename extensions", you'll see the .app extensions for all apps.
LIE #2: MAKING A DIRECTORY LOOK LIKE A FILE
An application is not a regular file, as it appears to be in the Finder, but a directory with special attributes and specific subdirectory structure. Such a directory is called a "bundle".
You can see the subdirectory structure in Terminal:
ls -l /Applications/Safari.app
ls -l /Applications/Safari.app/Contents
You can also see the directory structure in the Finder by right-clicking the application icon and selecting "Show Package Contents". You will see there is a subdirectory called "Contents", and within that there is a bunch of other stuff.
LIE #3: POSSIBLY A DIFFERENT NAME ALTOGETHER
Usually the Finder displays the name of the application as the directory name minus the ".app" extension. Thus, "Safari" instead of "Safari.app", "Contacts" instead of "Contacts.app", etc.
However, it is possible for applications to specify a different name to display in the Finder. The main reason for this is to localize the displayed application name. It is very rare to encounter this "lie" if English is your Mac's primary language.
Search for the term "CFBundleDisplayName" for the nuts and bolts of how developers get their apps to do this.