TweetFollow Us on Twitter

Using Repeat Loops in AppleScript

Volume Number: 20 (2004)
Issue Number: 12
Column Tag: Programming

AppleScript Essentials

by Benjamin S. Waldie

Should I Repeat Myself?

Using Repeat Loops in AppleScript

For the past couple of months, we have been talking about some basic Finder scripting. Now we are going to switch gears and get back to some basics of AppleScript. In this month's article, we will discuss the various types of repeat loops that you can use when you are scripting.

Why You Need Repeat Loops

Repeat loops are invaluable when writing AppleScript code, because you will frequently need to perform a single task more than once. While in some cases, you could simply write the same code over and over again in order to achieve the same result, in other instances, you cannot.

For example, let's say that you have a folder containing 10 files, and you want to rename all of them with a unique numeric extension from 1 to 10. You could write a repetitive AppleScript that would rename the files in this manner without a repeat loop. However, why would you want to do that? It would take a while to write, and it would be kind of a pain in the neck if you wanted to go back and change the code. For example, what if, after writing the code, you changed your mind and now you want the files to be named from 11 to 20? You would need to go back through all of your code and restructure it. Isn't one of the primary functions of AppleScript to automate things? So, why not automate your code?

In some cases, the only way to accomplish a task is to use a repeat loop. For example, let's say that you need a script that will rename files in a folder. However, the number of files in the folder may change each time the script is run. To do this, you would need to get a list of all of the files in the folder, and then use a repeat loop to go through and rename all of them.

As we continue, throughout this article, you will see how repeat loops can be extremely useful in all types of automated processes.

Types of Repeat Loops

There are several different types of repeat loops that can be used in AppleScript.

Repeat

In AppleScript, it is possible to loop indefinitely by using the repeat type of repeat loop, which is written as follows:

repeat
   -- DO SOMETHING
end repeat

Using the above example, the AppleScript code inside of the repeat loop will loop on forever. It will never stop unless an error occurs. You should take care when using this type of repeat loop, as you can sometimes box yourself into a corner with no way to get out. It is always good practice to provide some type of mechanism within your code in order to get yourself out of the repeat loop. This is typically done by using the exit repeat statement.

For example, let's say that you need to display a dialog prompting the user to enter a username. However, you want to make absolutely sure that the user types at least something into the dialog. This can be done with a combination of a repeat type of repeat loop and an exit repeat statement.

repeat
   display dialog "Please enter your username:" default answer ""
   set theUserName to text returned of result
   if theUserName <> "" then exit repeat
end repeat

As you can see in the example code above, the dialog will continue to be displayed until the user enters something into the prompt.

Repeat Times

Another type of repeat loop in AppleScript is the repeat times type of repeat loop, which is used to perform a loop for a specified number of times. For example, let's use the same scenario as above. However, instead of looping forever, let's say that you want to only give the user 3 chances to enter the username before an error will occur.

repeat 3 times
   display dialog "Please enter your name:" default answer ""
   set theUserName to text returned of result
   if theUserName <> "" then exit repeat
end repeat
if theUserName = "" then display dialog "Invalid Entry!!!"

In the example code above, the user will only be prompted to enter the username a maximum of 3 times. If the user does not enter a username, then an error notification will be displayed.

Repeat While

The repeat while style of repeat loop is typically used to test for a specific scenario to occur. For example, we could use the repeat while type of repeat loop as another way to verify that a user enters something into our dialog example.

set theUserName to ""
repeat while theUserName = ""
   display dialog "Please enter your name:" default answer ""
   set theUserName to text returned of result
end repeat

In the example above, the script will continue to loop until something is entered into the dialog. You could also use a repeat loop of this nature to loop until a file is detected in a certain folder. For example:

set theFilePath to (path to desktop as string) & "test.psd"
tell application "Finder"
   repeat while (file theFilePath exists) = false
   end repeat
end tell
display dialog "The Photoshop file has arrived!"

Repeat Until

The repeat until type of repeat loop is yet another type of repeat loop that is used to test for specific scenarios to occur. As you can see in the example code below, this type of repeat loop is very similar to the repeat while type of repeat loop.

set theUserName to ""
repeat until theUserName <> ""
   display dialog "Please enter your name:" default answer ""
   set theUserName to text returned of result
end repeat

Reprat With

The repeat with type of repeat loop can actually be broken down another level, into two separate types of distinct repeat with loops.

The first type of repeat with loop will allow you to loop for a specified number of times, while dynamically incrementing an integer variable's count. This type of repeat with loop is formed as follows:

repeat with theIncrementValue from theStartingValue to theEndingValue
   -- DO SOMETHING
end repeat

In the code above, the variable theIncrementValue signifies the current increment of an integer value in the loop. The variable theStartingValue signifies an integer that should be used as the initial increment value, whereas the variable theEndingValue signifies an integer that should be used as the final increment value. When a repeat loop of this nature is executed, it will continue to loop, incrementing the variable theIncrementValue each time until it reaches the value of the theEndingValue.

Let's take a look at another example in order to help illustrate this process. In the following example, we are going to prompt the user to select a folder, and then loop a specified number of times, building a folder for each increment.

set theDestinationFolder to choose folder
tell application "Finder"
   repeat with theIncrementValue from 1 to 10
      make new folder at theDestinationFolder with properties {name:theIncrementValue as string}
   end repeat
end tell

When executed, the code above will generate 10 folders, named from 1 to 10, in a user specified directory. You can see how using a repeat loop for this type of task can help to make your AppleScript code extremely efficient.

It is also possible to change the manner by which the increment in this type of repeat loop occurs. For example, you may not want to loop by 1's. Instead, you may want to loop by 2's. This can be done by adding an optional by parameter at the end of the initial repeat with statement. For example:

set theDestinationFolder to choose folder
tell application "Finder"
   repeat with theIncrementValue from 1 to 10 by 2
      make new folder at theDestinationFolder with properties {name:theIncrementValue as string}
   end repeat
end tell

In the example above, the script increments by 2's rather than 1's. Therefore, instead of building 10 folders, the script will only build 5, and they will be named "1", "3", "5", "7", and "9".

When using this type of repeat with loop, it is not necessary to begin the loop with a starting increment of 1. For example, the following code will cause 10 folders to be created, named from 11 to 20.

set theDestinationFolder to choose folder
tell application "Finder"
   repeat with theIncrementValue from 11 to 20
      make new folder at theDestinationFolder with properties {name:theIncrementValue as string}
   end repeat
end tell

It is also possible to cause the increment value to move in reverse, such as from 10 to 1. For example:

set theDestinationFolder to choose folder
tell application "Finder"
   repeat with theIncrementValue from 10 to 1 by -1
      make new folder at theDestinationFolder with properties {name:theIncrementValue as string}
   end repeat
end tell

At the beginning of this section, I mentioned that there are actually two types of repeat with loops in AppleScript. The second type of repeat with loop is used to loop through a series of values in a list. It is formed as follows:

repeat with theCurrentValue in theListOfValues
   -- DO SOMETHING
end repeat

When using this type of repeat with loop, each time the code loops, the variable theCurrentValue will take on the value of the current item in the list variable theListOfValues. Let's take a look at this type of loop in action.

set theDestinationFolder to choose folder
set theListOfValues to {"apples", "oranges", "pears"}
tell application "Finder"
   repeat with theCurrentValue in theListOfValues
      make new folder at theDestinationFolder with properties {name:theCurrentValue}
   end repeat
end tell

In the example code above, the script will loop through the list variable theListOfValues, which, in this case, contains the names of three different types of fruit. Each time the code loops, the variable theCurrentValue will take on the current value from the variable theListOfValues. So, during the first loop, the variable theCurrentValue would take on a value of "apples", the second loop, it would take on a value of "oranges", and so forth.

In Closing

Hopefully, the various types of repeat loops specified in this article will be helpful to you as you begin writing more complex AppleScript code. By creating nested repeat loops of varying types, you can really create some complex and adventurous scripts.

If you are interested in learning more about repeat loops in AppleScript, I recommend checking out the AppleScript Language Guide, which can be found under AppleScript in the Developer Connection on Apple's web site - http://developer.apple.com/. You may also want to consider picking up a good introductory AppleScript book, such as Danny Goodman's AppleScript Handbook.

Until next time, keep scripting!


Benjamin Waldie is president of Automated Workflows, LLC, a firm specializing in AppleScript and workflow automation consulting. In addition to his role as a consultant, Benjamin is an evangelist of AppleScript, and can frequently be seen presenting at Macintosh User Groups, Seybold Seminars, and MacWorld. For additional information about Benjamin, please visit http://www.automatedworkflows.com , or email Benjamin at applescriptguru@mac.com.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Splash Cars guide - How to paint the tow...
Splash Cars is an arcade driving game that feels like a hybrid between Dawn of the Plow and Splatoon. In it, you'll need to drive a car around to repaint areas of a town that have lost all of their color. Check out these tips to help you perform... | Read more »
The best video player on mobile
We all know the stock video player on iOS is not particularly convenient, primarily because it asks us to hook a device up to iTunes to sync video in a world that has things like Netflix. [Read more] | Read more »
Four apps to help improve your Super Bow...
Super Bowl Sunday is upon us, and whether you’re a Panthers or a Broncos fan you’re no doubt gearing up for it. [Read more] | Read more »
LooperSonic (Music)
LooperSonic 1.0 Device: iOS Universal Category: Music Price: $4.99, Version: 1.0 (iTunes) Description: LooperSonic is a multi-track audio looper and recorder that will take your loops to the next level. Use it like a loop pedal to... | Read more »
Space Grunts guide - How to survive
Space Grunts is a fast-paced roguelike from popular iOS developer, Orange Pixel. While it taps into many of the typical roguelike sensibilities, you might still find yourself caught out by a few things. We delved further to find you some helpful... | Read more »
Dreii guide - How to play well with othe...
Dreii is a rather stylish and wonderful puzzle game that’s reminiscent of cooperative games like Journey. If that sounds immensely appealing, then you should immediately get cracking and give it a whirl. We can offer you some tips and tricks on... | Read more »
Kill the Plumber World guide - How to ou...
You already know how to hop around like Mario, but do you know how to defeat him? Those are your marching orders in Kill the Plumber, and it's not always as easy as it looks. Here are some tips to get you started. This is not a seasoned platform... | Read more »
Planar Conquest (Games)
Planar Conquest 1.0 Device: iOS Universal Category: Games Price: $12.99, Version: 1.0 (iTunes) Description: IMPORTANT: Planar Conquest is compatible only with iPad 3 & newer devices, iPhone 5 & newer. It’s NOT compatible with... | Read more »
We talk to Cheetah Mobile about its plan...
Piano Tiles 2 is a fast-paced rhythm action high score chaser out now on iOS and Android. You have to tap a series of black tiles that appear on the screen in time to the music, being careful not to accidentally hit anywhere else. Do that and it's... | Read more »
Ultimate Briefcase guide - How to dodge...
Ultimate Briefcase is a simple but tricky game that’s highly dependent on how fast you can react. We can still offer you a few tips and tricks on how to survive though. Guess what? That’s exactly what we’re going to do now. Take it easy [Read more... | Read more »

Price Scanner via MacPrices.net

12-inch 1.2GHz Silver Retina MacBook on sale...
B&H Photo has the 12″ 1.2GHz Silver Retina MacBook on sale for $1399 including free shipping plus NY sales tax only. Their price is $200 off MSRP, and it’s the lowest price for this model from... Read more
iPads on sale at Target: $100 off iPad Air 2,...
Target has WiFi iPad Air 2s and iPad mini 4s on sale for up to $100 off MSRP on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale prices for... Read more
Target offers Apple Watch for $100 off MSRP
Target has Apple Watches on sale for $100 for a limited time. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: - Apple... Read more
Apple refurbished 2014 13-inch Retina MacBook...
Apple has Certified Refurbished 2014 13″ Retina MacBook Pros available for up to $400 off original MSRP, starting at $979. An Apple one-year warranty is included with each model, and shipping is free... Read more
Macs available for up to $300 off MSRP, $20 o...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free, and... Read more
Watch Super Bowl 50 Live On Your iPad For Fre...
Watch Super Bowl 50 LIVE on the CBS Sports app for iPad and Apple TV. Get the app and then tune in Sunday, February 7, 2016 at 6:30 PM ET to catch every moment of the big game. The CBS Sports app is... Read more
Two-thirds Of All Smart Watches Shipped In 20...
Apple dominated the smart watch market in 2015, accounting for over 12 million units and two-thirds of all shipments according to Canalys market research analysts’ estimates. Samsung returned to... Read more
12-inch 1.2GHz Retina MacBooks on sale for up...
B&H Photo has 12″ 1.2GHz Retina MacBooks on sale for $180 off MSRP. Shipping is free, and B&H charges NY tax only: - 12″ 1.2GHz Gray Retina MacBook: $1499 $100 off MSRP - 12″ 1.2GHz Silver... Read more
12-inch 1.1GHz Gray Retina MacBook on sale fo...
B&H Photo has the 12″ 1.1GHz Gray Retina MacBook on sale for $1199 including free shipping plus NY sales tax only. Their price is $100 off MSRP, and it’s the lowest price available for this model... Read more
Apple now offering full line of Certified Ref...
Apple now has a full line of Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Subject Matter Expert - Experis (Uni...
This position is for an Apple Subject Matter Expert to assist in developing the architecture, support and services for integration of Apple devices into the domain. Read more
*Apple* Macintosh OSX - Net2Source Inc. (Uni...
…: * Work Authorization : * Contact Number(Best time to reach you) : Skills : Apple Macintosh OSX Location : New York, New York. Duartion : 6+ Months The associate would Read more
Computer Operations Technician ll - *Apple*...
# Web Announcement** Apple Technical Liaison**The George Mason University, Information Technology Services (ITS), Technology Support Services, Desktop Support Read more
Restaurant Manager - Apple Gilroy Inc./Apple...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.