Mac OS X Leopard - ARCAism

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CHAPTER 23 MAC OS X AUTOMATION WITH AUTOMATOR AND APPLESCRIPT
AppleScript is quite loose, with several ways to say the same thing. The problem is, this leaves
you guessing at the proper way to say something, with many grammatical constructions that
seem like they should work but don’t.
Hence, AppleScript tends to happen organically, with each phrase leading to a compile and
test. If you’re used to banging out pages of code between runs, you might want to reconsider that
habit, or learning AppleScript is going to be a painful experience.
Analyzing the Code
Although AppleScript and Automator accomplish similar things, they don’t exactly translate
back and forth, so we have to do some things a little differently. It’s probably best to just run
through the code sample and point out some sights along the way.
Comments in AppleScript are preceded by --, like so:
-- Remove any existing images
Since it is mainly concerned with controlling applications, the central syntax element of an
AppleScript program is the tell block:
tell application "Finder"
Each application’s vocabulary is contained in a special dictionary file. When working with
an application in AppleScript, the first thing you should do is open its dictionary by selecting
Open Dictionary... from the File menu or by typing Shift+Cmd+O.
Variables can be named on the fly. Their values are set with the set...to construct:
set _imageFolder to path to pictures folder
There is no real way of telling what’s a variable and what’s a keyword, so we like to precede
our variables with an underscore. That’s just a personal preference, though.
The path to construct locates known folders. In this instance, we’re trying to get a path to
the user’s Pictures folder, which in UNIX terms we would call ~/Pictures.
Literal terms are enclosed in quotation marks, as are strings:
set _imageFolder to folder "Keyword Screensaver" of folder _imageFolder
Most objects on the system are considered containers for other objects. A folder that’s inside
another folder is of that folder. The of form can be extended to a ludicrous degree. You could
refer to a character of a word of a paragraph of a document of an application, and so forth. You
can also use the possessive form:
set _imageFolder to _imageFolder's folder "Keyword Screensaver"
AppleScript is a lot like LISP in that its only real data structure is the list. This underlies constructs
like this:
delete every file in _imageFolder
You can also refer to things like the first file in the folder or file 3 in the folder. AppleScript
also has explicit looping constructs, as you’ll see later.
AppleScript is not whitespace sensitive, but it does use newlines to end its statements. Multiline
syntax structures, such as tell blocks, require end statements:
end tell
As a testament to the flexibility of the AppleScript language, the entire first tell block could
also have been written as a single line: