Scripting Basics

The following notes provide a bare outline of the object-oriented programming (OOP) language known as AppleScript. For further information, see the AppleScript Language Guide (Addison-Wesley 1993), a scholarly although rather tedious tome.

The author originally found this language difficult, perhaps due to his familiarity with calculus and BASIC programming. In some areas, the coercions between different object types (such as text and date) seem inconsistent while the setting up of error handling can be very frustrating.

Here’s an embellished script that empties the Trash without leaving the current application, with comments in lines that have a -- prefix:-

• To use a script from inside the front application, just choose Save in Script Editor and select Compiled Script in the Format menu. You can then place the resultant script in the required location for your script-launching software and launch it when needed.

The above example includes the following features found in most scripts:-

• An instruction to a scripting addition, in this case display dialog
• The use of if, end if, with timeout and end timeout statements
• Instructions to an application, in this case the Finder, inside tell and end tell statements
• The inclusion of blank lines to improve presentation
• Two methods of entering comments

A simple script, which contains only one section, usually works by what is known as an implied run command. For more complex scripts, which usually incorporate subroutines, an actual run command must be used to identify the main part of the script, in the form shown below:-

When a script is used as a droplet it must also have special subroutine called open to open those items that are dropped onto it. This should be in the form shown below. In this instance the run routine also calls the open subroutine, thereby avoid any unnecessary duplication of script.

• The line set itemList to itemList as list ensures the droplet works normally when only one item is dropped onto it.

The script shown below uses an open subroutine to process items that have already been selected on the desktop or chosen via an Open dialogue. This particular example gives the name of each item.

Note the the use of a count instruction that checks how many items have been selected and the repeat loop around the choose file line, which allows several items to be selected in turn. Finally, the tell me to open statements instruct the script to open the chosen items, not the Finder. If you don’t use tell me the Finder opens the items in the normal way.

In the above example, the open subroutine includes a parameter in brackets. Other subroutines often involve several parameters, or none at all. Even if you don’t use any parameters you must still use brackets, as in mySubroutine().

Error Handling

Under normal circumstances, a failed script produces a special AppleScript error dialogue that contains an error message, sometimes accompanied by an error number, as shown below:-

Usually, clicking on the Edit button causes Script Editor to launch, revealing the error as highlighted text. As you can see, this kind of dialogue is rather ugly and the messages can be confusing, although they’re useful during debugging. They also encourage other people to tinker with your scripts.

• Click here to see some of the common AppleScript error numbers. When you’ve finished looking at the table simply click on your browser’s Back button to return to this page.

Fortunately, AppleScript has a mechanism for using standard dialogues or removing them altogether. This is achieved by wrapping the entire script (or a selected portion of a script) inside try and end try statements, as in the following, where * ** *** is the script that can cause an error:-

In this case errors shown in the resultant dialogues contain both the error message and error number:-

The following example displays the message on its own:-

as shown here:-

whilst this version shows a generic message for all errors:-

which looks like this:-

Sometimes, you may want to generate error messages that vary according to what happens, whilst leaving AppleScript free to insert its own messages. Here’s an example:-

If a script is intended to produce observable effects you can prevent all error messages with a script of the form:-

If your try and end try statements enclose part of a script you can force it to quit by using something like:-

which effectively converts all errors into error number -128, the user cancelled error. The following is similar, but doesn’t produce a message:-

The nesting of error statements can be useful, as in this example:-

However, there’s a problem: the outer error handling produces a ‘user cancelled’ message whenever an inner error occurs. This can be prevented by modifying the last section to something like:-

Dummy Error Numbers

In some instances you may want to generate your own error numbers, as in:-

or as in:-

Generally speaking, you can use any value from 500 to 10000 as an error number.

Objects

Traditional programming, such as BASIC, uses variables to store numbers and text within a program. AppleScript, in common with other OOP languages, extends this to refer to objects, such as files, disks and computer ports. In AppleScript terminology an object is known as a value, although the author prefers the familiar ‘object’ term.

AppleScript supports 14 types or classes of object, each known as an object type or value class, as listed below:-

Although most applications handle all classes, some prefer to use their own varieties. For example, ClarisWorks requires you to use the plain text class instead of the string class in scripts.

Coercions

Some values can be coerced into other classes. For example:-

gives a result in the form of "Tuesday, February 10, 1998​ 4:51:49 pm".

• Some scripting additions provide extra coercions not directly supported by AppleScript.
• Click here to see the coercions in AppleScript 1.8.3, as well as those provided by the Akua Sweets 1.4.2 scripting addition. Most of the coercions supported by the latter involve special classes whose names incorporate uppercase letters. When you’ve finished looking at the table simply click on your browser’s Back button to return to this page.

Object Names

The name of an object mustn’t correspond to any keyword used in AppleScript, or to those used in a scripting addition or application. Most are easily avoided, although some are tricky to spot.

Object names names with capitals inside, such as theDiskSizeInKB, are often used, although some scripting additions also use these kinds of words. Names such as the_disk_size_in_KB are usually suitable, although they aren’t easy to read.

• AppleScript doesn’t distinguish between uppercase and lowercase letters in object names.

Set and Copy

Values are usually defined using set or copy, as in:-

The set instruction can also be used to ‘initialise’ a value at the start of a script.

A full understanding of the difference between set and copy instructions can avoid unnecessary complications. For example, in the following script:-

both listOne and listTwo end up containing {4,5,6}, since the second line has made both values equal. If you don’t want this to happen you should use copy instead, as shown below:-

In this case listOne contains {4,5,6} and listTwo contains {1,2,3}.

The various methods of manipulating values are too numerous to describe in this guide. However a few examples are given below. The following script gets the second word of this text:-

this script obtains the length of a list:-

and this selects the third item in a list:-

Co-ordinates

Sometimes, it’s necessary to specify the size and position of a window or some other kind of rectangle. The size alone can be given by means of a two-item list such as {200, 100}, which specifies a rectangle of 200 × 100 pixels. Note that the width of the rectangle along the horizontal axis (the x value) is always given before the height along its vertical (the y value).

Defining both the size and position of a rectangle is slightly more difficult, requiring you to use a set of four co-ordinates. Generally speaking, these are measured from a zero point, located at the bottom left-hand corner of the screen or area under consideration. To add to the confusion, the size of a dialogue on a computer screen is normally measured from the top left-hand corner of the screen.

Co-ordinates are often given as a list in the form of {left, top, right, bottom}, which can be written as {x1, y1, x2, y2}, although the ordering of the latter isn’t entirely logical when working with co-ordinates that refer to the bottom left-hand corner. Here’s an example:-

which can be specified using co-ordinates of {6, 17, 28, 7}.

Properties

The initial contents of a value can be set using a property statement at the start of a script, such as:-

Note, however, that the contents of values defined in this way are ‘remembered’ each time the script is used. For example, if you run a script and testFlag ends up as true this value will again be used when you next run the script. Similarly, the following script tells you how many times it has run:-

Standard Instructions

The common instructions used in AppleScript can be divided into the following groups:-

Conditional Statements

These let you make decisions in a script, often involving if, else and end if commands, as in:-

although simple one-line statements can also be used, such as:-

Control statements

These determine the flow of a script, depending on a result. They often involve the use of tell, if, repeat or try statements, as well as matching end statements.

Examples of such statement have already appeared in this document. Here’s another one:-

This kind of repeat statement is rather dubious, since there’s a distinct risk of getting stuck in an endless loop. This can be fixed by adding a conditional statement inside the loop, as in:-

although it’s far better to to include a conditional value in the top line, as shown in these examples:-

Finally, there’s the most complex form of repeat statement:-

Subroutines

This portion of script performs the same action within different parts of any script, making it easy to create short and well-organised scripts. Each subroutine begins with on followed by the routine’s name and ending with a matching end statement. Here’s a routine that converts a list to text:-

where the parameter called theList is the actual list and theDelim is the delimiter used in the list. You can ‘call up’ such a routine from within the main part of your script using a line such as:-

Arithmetical Operations

The following mathematical functions are built into AppleScript:-

Brackets can be used to improve the presentation of operations, although you should remember than items within an innermost parenthesis are always calculated first. This example uses a routine to find the impedance of an 10µH inductor with a DC resistance of 0.5 Ω at a frequency of 1000 Hz:-

Text Manipulation

AppleScript provides little in the way of built-in support for modifying text, although you can create your own routines You can also manipulate text by changing the delimiters used for separating text items, as in this example, which extracts the name of a file from its path:-

The try statement around the main part of this script is essential. If you don’t include this and the script fails, AppleScript continues to use the new delimiter in all subsequent scripts. For this reason, it’s better to use something like this:-

which, although much more complicated, is actually shorter.

Selecting large amount of text within a script can cause memory problems, as in this example:-

where the script has to process the actual text data. To avoid this, you can use:-

which instead works out the length of the text.

AppleScript often can’t perform operations on text over 32 KB, although this is usually possible if left to a scriptable application with sufficient memory. And there shouldn’t be any problem transferring data via the clipboard or other files.

Simple Application Commands

Depending on scriptability, you can send each application a range of instructions. However, if the application name entered in a script doesn’t match the real name or the script can’t locate its file, AppleScript puts up a Where is the file? dialogue, allowing you to find the file manually. Having done this and re-compiled the script you shouldn’t need to do it again.

Any application, even if it isn’t scriptable, can be launched using a script of the form:-

In the case of scriptable applications you can also use a line of the form:-

or:-

Note that the tell command forces any enclosed operations to be executed from within the application’s memory space, which can cause problems, especially in Mac OS 8.5. And, in all versions of the Classic Mac OS, you can’t normally use a general command, such as display dialog, inside a tell statement unless the command is understood by the application.

• When creating a script you can use app as a shortcut for the word application.

You can quit any application using a command in the form of:-

The launch command is slightly different, since the application doesn’t show all of the usual start-up displays when it’s launched. The actual line of script is:-

The following variation is only suitable for scriptable applications, although it may cause the application to quit and relaunch if it’s already running:-

The following kind of script usually works, but only with a scriptable application:-

At this stage, some people express confusion over the word alias. However, in this context the term refers to an AppleScript alias, not a standard Mac OS alias. This kind of alias refers to a specific file and keeps track of it, even in the event of it being moved or receiving a new name.

If the above script succeeds, it launches the application and the file’s window appears. Note however, that the application may not come to the front, in which case you'll need to add an extra line containing activate after the existing one containing launch. Some applications can open a list of files, as in:-

Note that this particular application doesn’t need the word alias to follow an open instruction.

• Some applications don’t need an activate instruction and can object to the use an activate or launch command.

Introduction to the Scriptable Finder

The Finder accepts similar commands to those used by applications. However, an open command that’s sent to the Finder shouldn’t be confused with the standard AppleScript open command. The latter opens files that are dropped onto a script in the form of a droplet.

The following example opens a file using Netscape, which is identified by a creator code of MOSS:-

whilst this form of script opens a particular file using its default application :-

while this opens a list of files:-

The Finder can perform numerous other tasks. For example, this line of script enters the name of a Mac OS computer’s startup disk into a value called sysDisk:

whilst this script moves a file identified as theFile to the path given in theFldr:

The replacing instruction indicates that an existing file of the same name must be replaced. A similar script can copy a file:-

The Finder can also create new files from scratch, as in the following:-

This example produces a Stickies text file, which is identified by creator code of notz and file type of TEXT. The new file’s filename should be contained in the value fileName.

Scripting Additions

Recent versions of the Classic Mac OS include a Standard Additions scripting addition, which lives in the Scripting Additions folder, inside the System Folder, replacing the older additions used in earlier versions of the system. Further additions can be added, as required.

The following information refers to the Standard Additions file:-

Dialogues

The most useful feature provided in Standard Additions is a dialogue box. By default, this contains up to 255 characters of text, a Cancel button and an OK button. For example, the line:-

provides the following dialogue:-

If you click the Cancel button the script invariably quits. The limitation of 255 characters can be a problem, with excessively long text becoming harmlessly truncated, as in this example:-

It’s also possible to define up to three individually named buttons, as in:-

which gives this dialogue:-

The default button can be selected by name or number as in:-

or:-

both of which give:-

To make the script to continue even though Cancel has been selected you must add a space before and after Cancel, as in:-

the spaces before and after the word ensuring that it aligns centrally in the button.

You can also create a dialogue that accepts entries, such as:-

which appears as:-

The result produced by such a dialogue can be extracted using:-

The entered string will be contained in the value theTxt.

If you need to know both the string and the name of the button that was clicked you should use something like:-

which can be shortened to:-

Similarly, if you want the result as an integer instead of text you could use:-

In this case, AppleScript’s default value, known as result, has been used in place of the theDlg object in the previous example. Although, this is simpler it doesn’t indicate which button was clicked.

Dialogues can also be used to escape from a loop, as in this script:-

The appearance of text entries for a dialogue can often be improved by incorporating return in the text, as in this example:-

which gives the dialogue shown below:-

The keyword tab, although acceptable in text strings, only acts as a space character in dialogues. However, the use of icons in dialogues is highly recommended, as in this an example:-

which gives:-

You can replace caution by note for the ‘speaking man’ icon or by alert for the ‘warning hand’ icon. Similarly, other icons can be addressed by number, as in this script:-

which appears as:-

The icons provided by Classic Mac OS 9.1 are shown below:-

These icons are stored as ICON or cicn resources in modern versions of the System file. You can also call up icons from within an application from within a tell statement. Applications usually have a standard icon identified by the number 128.

Other Commands

As well as providing dialogues, Standard Additions can convert values to and from their ASCII equivalents or find offsets within a string. Here’s an example:-

The same addition can also be used to handle files and folders, as in this example that uses the choose file and list folder commands to open the files in a chosen folder:-

There’s also a path to command, which can give the location of the front application’s file or the script’s applet file, depending on where the current script is running from:-

As usual, the as text instruction coerces the result into a string. In the next example path to is used to locate the Temporary Items folder in the Classic Mac OS:-

Finally, the say instruction lets you send instructions to the MacinTalk speech synthesiser, also allowing you to increase or reduce the emphasis of particular words, as in this example:-

©Ray White 2004.