The flow-control statements in
AppleScript orchestrate the “flow”
or the order in which the code statements execute in your scripts.
Programmers will be familiar with AppleScript’s
if conditional statements, which are very similar
to the syntax of Visual Basic, Perl, and other languages. These
statements execute code only if the tested conditions are
true. AppleScript handles loops in script code
with several variations of the repeat statement,
similar to the “for,”
“foreach,” or “for
each” statements in other languages. The
repeat flow-control construct repeats the
execution of code a specified number of times or for each member of a
container, such as a list type. Or, it repeats a
code phrase a specified number of times:
repeat 100 times...end repeat
You will be
pleased to know that AppleScript has more than adequate
error-trapping capabilities. This is accomplished by enclosing the
statements that may raise errors in a try...end try statement block. In addition, you have already seen
dozens of examples of the tell..end tell statement
in earlier chapters. These statements specify the objects, usually
application objects, that receive the commands or Apple events that
your script sends. You specify the targets of different script
commands by using these tell statements.
You can nest flow-control statements within other flow-control
statements. Most of these statements end, appropriately, with the
reserved word end, optionally followed by the
statement identifier, such as tell or
repeat. An example is:
tell app "Photoshop 5.5"...end tell
The if and tell statements
allow “simple” rather than
“compound” usage, such as:
if (current date) > date "1/1/2001" then display dialog "Welcome to 2001"
These simple statements appear on one line, they do not contain other
code statements, and they do not need to be completed with the
end reserved word. This code shows some nested
flow-control statements and simple statements:
tell application "Finder"
set freeMemoryBlock to largest free block
(* Here's a simple statement; no 'end' is necessary *)
if freeMemoryBlock < 10000000 then display dialog¬
"Memory is getting low"
set listOfProcesses to name of processes
if "BBEdit 5.0" is not in listOfProcesses then (* compound 'if'
statement *)
tell application "BBEdit 5.0" to run -- simple 'tell' statement
end if
end tellSuffice it to say, flow-control statements are how AppleScript derives much of its power and complexity. You will develop very few scripts that do not use at least one flow-control statement. Table 7-1 lists the statements that this chapter describes.