AppleScript: The Definitive Guide, 2nd Edition

Variable Names

The name of a variable must begin with a letter or underscore and must consist entirely of alphanumeric or underscore characters. So a variable name must begin with a character in the character set [a-zA-Z_] and must consist entirely of characters in the character set [a-zA-Z0-9_].

Case-Insensitivity of Variable Names

Variable names are case-insensitive at compile time. That means the following code will compile and run:

set myVar to 5
set myvar to myvar + 1

AppleScript assumes that myvar in the second line is the same variable as myVar in the first line. Furthermore, as a reflection of this assumption, AppleScript rewrites the variable names after compilation (that is, during decompilation) so that their case matches the first usage of the name:

set myVar to 5
set myVar to myVar + 1

This phenomenon suggests a trick that can help you spot mistakes: when you first define a variable, use an uppercase letter in its letter; elsewhere, never use an uppercase letter in a variable name. Then, after compilation, any variable name without an uppercase letter must be a mistake. For example, here's some code that I typed following these rules, before compilation:

set myVar to 5
set mybar to myvar + 1

Here's the same code after compilation:

set myVar to 5
set mybar to myVar + 1

In that code I have accidentally created and set the value of an unwanted variable mybar in the last line. I meant to say myvar, but I mistyped it. This won't cause AppleScript to generate any error, and the script ...