AppleScript: The Missing Manual

Chapter 14. Testing and Debugging Scripts

At some point, you’re bound to write a script that misbehaves. Maybe you’ll forget to press Return after a line of code, or you’ll accidentally use if when you mean to use repeat. Either way, your script won’t work the way you want it to, and you’ll waste several minutes—or longer—trying to track down the problem.

Fortunately, AppleScript has several tools for fixing scripts. Some, like the AppleScript compiler (see below), make sure that your script works before you try to run it. Other tools, like the Xcode debugger (Section 14.5), let you track down errors while your script is running. No matter what tool you use, you’re never left to hunt for errors alone.

Note

The example scripts from this chapter can be found on the AppleScript Examples CD (see Sidebar 2.1 for instructions).

First Line of Defense: The Compiler

When you click the Run button in Script Editor, the first thing that happens is your script gets compiled. That’s AppleScript’s way of finding typos, misplaced punctuation, and so on. If AppleScript finds an error, you’ll see a dialog box like the one in Figure 14-1. Otherwise, your script proceeds to its regularly scheduled commands.

Unfortunately, AppleScript compiler errors are notoriously hard to decipher. Unless you have a Ph.D. in programmer-ese, therefore, Table 14-1 will be of great assistance in your compiling adventures.

Table 14-1. Common AppleScript compiler errors

Error message	Code that would produce it	What’s the problem? ...