TweetFollow Us on Twitter

December 95 - MPW Tips and Tricks: ToolServer Caveats and Carping

MPW Tips and Tricks: ToolServer Caveats and Carping

Tim Maroney

MPW comes with dozens of useful tools and scripts. They're handy for a lot of things besides programming -- or would be, if you were willing to keep the MPW Shell open all the time, and if they weren't based on command lines. Fortunately, the Shell is not the only way to use them: a small application known as ToolServer makes it possible to run MPW commands in a standalone mode. You can write double-clickable MPW scripts, give MPW commands from AppleScript, and write front ends to tools in high-level programming languages.

Using ToolServer isn't exactly like using the MPW Shell. There are caveats if you want to write scripts and tools that will work in both environments. We'll first take a look at these issues and then explore how to package commands for use with ToolServer.

MODULARITY AND FACTORING

Shell scripting languages such as sh and csh in UNIXreg., as well as MPW, have always taken a rather cavalier approach to code organization. Most configuration is achieved with a global namespace of environment variables. This is a problem with ToolServer, because you don't want to load your entire set of MPW startup scripts every time you run a command. Even if you wanted to, you couldn't -- ToolServer doesn't have text editing, menu bar customization, or other user interface elements of the MPW Shell, so it's missing several built-in commands. Your existing startup scripts won't work, and some utility commands may also fail.

Three principles from structured software design are useful here:

  • Separate user interface code from core code.

  • Use the "include" mechanism to provide modularity.

  • Reduce dependencies between modules.
Let's take a concrete example. Many of us cut our teeth as programmers on UNIX. Initiates of this brilliant but byzantine operating system tend to grow fond of its command set, in much the same way that cabalists become attached to bizarre metaphysical formulas purporting to explain the universe. A UNIX wizard's MPW startup script usually contains a list of aliases to translate between UNIX and MPW: Alias ls Files, Alias cp Duplicate, and so on. These commands are then used in all the wizard's utility scripts as well. This creates a problem with ToolServer: it can't use these startup scripts because they also customize the user interface with commands like AddMenu and SetKey. Without the aliases, though, the utility scripts won't run.

One solution to this problem combines the first two principles listed above. First, separate the aliases from the user interface setup code, yielding two different startup files. Both files are invoked by the MPW Shell startup process but neither is invoked at ToolServer startup. Second, instead of assuming a particular global configuration, make each utility script explicitly include whatever setup files it may require. MPW's analog of the #include directive of C is Execute, which executes a file in the current namespace.

We can apply common C bracketing conventions to avoid multiple inclusion of the same file. Assuming that our UNIX wizard has split off his or her aliases into a file named UNIXAliases, a script using these aliases would start -- after the header comment -- as follows:

if {__UNIXALIASES__} == ""
   execute UNIXAliases
end
The script file UNIXAliases would set the variable __UNIXALIASES__ to something other than the empty string, and decline to execute itself again if it had already been executed, like so:
if {__UNIXALIASES__} == ""
   set __UNIXALIASES__ "true"
   ... # the aliases go here
end # __UNIXALIASES__
A different solution to the same problem involves the third principle, reducing dependencies between modules. Utility scripts don't really need to use csh commands, after all: the aliases are there mostly so that the wizard can type them into the MPW Shell, his or her fingers having long ago locked into an inflexible pattern of TTY interaction. If scripts don't assume the availability of a different command set -- that is, if they stick with the MPW command names -- the aliases need not be included at all.

Independence is a good idea for another reason: you may give your ToolServer scripts to other people at some point in your long and happy life. The more your commands depend on the global environment, including ToolServer startup files, the more likely they are to conflict with another user's environment.

INPUT AND OUTPUT

ToolServer implements most of the MPW Shell's I/O system, which is based on the stdio library and UNIX-style redirection. However, it doesn't read keyboard input or display text output. All of its I/O channels are ultimately files, pipes, or the pseudodevice Dev:Null.

The only mechanisms for interacting with the user in ToolServer are commands like Alert and Confirm that display dialog boxes, and interface tools you write yourself. Even these must be used with caution, since ToolServer can run remotely over a network, and hanging a server machine by bringing up a dialog box is often regarded as undesirable.

It helps to separate user interface code from core code, as already discussed. Commands you intend to run with ToolServer should not have a user interface: they should perform an action that's completely specified by their command line. An outermost user interface script can present choices to the user, then invoke an innermost command that has no user interface. The outermost script is just for ToolServer; the inner script or tool is suitable for both ToolServer and the MPW Shell.

You can detect when a command is running under ToolServer and squelch its user interface by looking at the environment variable BackgroundShell. This is the empty string when running under the MPW Shell, but it's nonempty under ToolServer. Most user interactions in MPW commands are just confirmation alerts, so if execution reaches a Confirm command and BackgroundShell is set, assume that the user would answer "no." All commands that require confirmation should support the -y and -n options, which provide answers on the command line, and these options should be provided when the commands are used from ToolServer.

Some MPW commands, such as Make and Backup, write output to the Worksheet, and the user then selects and executes the output. This model doesn't apply to the ToolServer environment since it has no Worksheet. The easiest solution is to redirect the command output to a temporary file, execute that file, and then delete it. This is less selective than using the Worksheet, which allows the user to decide which lines to execute. If selectivity is important, you can write a command that presents the lines of output to the user and allows them to be independently accepted or rejected.

We don't live in the best of all possible worlds, St. Thomas Aquinas and Dr. Pangloss to the contrary, and so commands often return errors. These generate text that's directed to the standard error channel. In the MPW Shell, error text goes to the frontmost window by default, but in ToolServer, the default is a file named command.err in the folder containing the command file. This is very antisocial behavior, especially since commands invoke other commands and the error file could wind up buried at some arbitrary-seeming place in your folder tree. Redirect the standard error channel to save yourself from Sisyphean levels of frustration whenever something goes just a little bit wrong.

There are two ways to redirect errors. First, you can use the standard MPW error redirection characters >=, >=>=, [[Sigma]], and [[Sigma]][[Sigma]] in your outermost user interface script. For instance, the script line

Veeblefetzer >= "{Boot}"Veeblefetzer.Errors
would redirect errors to the file Veeblefetzer.Errors at the top level of your startup disk. This does little or nothing to bring the errors to your attention, though, so your outermost script should look something like this:
Set ErrorFile "{TempFolder}"MyUtility.Errors
Delete -i "{ErrorFile}"
Set Exit 0 # Don't bomb quietly on errors
Potrzebie >=>= "{ErrorFile}"
if {Status} == 0
   Veeblefetzer >=>= "{ErrorFile}"
end
if `Exists "{ErrorFile}"`
   Alert `Catenate "{ErrorFile}"`
   Delete -i "{ErrorFile}"
end
The other way to redirect errors is to set the ToolServer built-in variable BackgroundErr to the name of a file. This will create that file whenever there's an error. This is somewhat less flexible than redirection, but it can be set once and for all in a ToolServer startup script. That would make the script above read like this:
Delete -i "{BackgroundErr}"
Set Exit 0 # Don't bomb quietly on errors
Potrzebie
if {Status} == 0
   Veeblefetzer
end
if `Exists "{BackgroundErr}"`
   Alert `Catenate "{BackgroundErr}"`
   Delete -i "{BackgroundErr}"
end
Standard output can be controlled similarly, using either redirection characters or the environment variable BackgroundOut.

FORMS OF TOOLS

There are several ways to package commands for use with ToolServer. The most basic and boring ways are:
  • Use the Execute Script command in ToolServer's File menu to select and execute a script file.
  • Drop a script file on the ToolServer application icon.
  • Give the "ToolServer [script ... ]" command in the MPW Shell.
There are more interesting deployment modes, but they require a bit more explanation.

Standalone scripts. If you change the creator of a script file to 'MPSX', double-clicking it in the Finder will launch ToolServer and send it an Open Document event, causing it to be executed. Use this approach for your outermost user interface scripts. To change the creator, use MPW's "SetFile -c 'MPSX' file" command.

There is, alas, no such thing as a standalone tool, but you can write a one-line script that invokes a tool with any parameters or none.

AppleScript. ToolServer is fully scriptable. Aside from the four required commands, it has only one scripting command, the dreaded DoScript. This takes a command written in another scripting language --  MPW command language in this case -- and passes the command to its script interpreter. DoScript is discouraged in new applications because it's unstructured, but it's very useful for pre-AppleScript applications that have their own languages.

A simple AppleScript script confers few benefits over a standalone ToolServer script. In fact, it's better to avoid mixing scripting languages if you can. However, using FaceSpan or another AppleScript authoring tool, you can use AppleScript to set up a conventional application that relies on ToolServer as a workhorse. Simply pass DoScript commands in response to user actions, redirecting errors and output to temporary files that you interpret in your AppleScript code.

Apple events. Finally, you can take AppleScript one step further, driving ToolServer directly with Apple events generated from compiled software. This delivers the maximum in flexibility and performance. You could even write a project-file development system based on MPW compilers. Another possibility would be HyperCard XCMDs, allowing MPW commands to be invoked from HyperTalk. An Apple event front end could be created for a particular MPW tool, allowing it to be cleanly invoked from other scripts or compiled software; this might also provide a simple user interface for controlling it with dialogs and menus.

ToolServer accepts the required Apple events, as well as DoScript and some special-purpose events related to status checking, command canceling, and error and output redirection. These are documented in Chapter 4 of the ToolServer Reference manual that comes with MPW. In this column in the last issue of develop, I provided sample code for interacting with SourceServer (another Apple event-driven MPW Shell subset), and that code can easily be adapted for ToolServer.

TOOLS FOR THE FUTURE?

Because it's tied to a command-line interface, the MPW toolset has come to seem rather archaic, but there's life in the old girl yet. ToolServer's support for Apple events and AppleScript allows innumerable improvements in its interface. In the future, we may see friendly front ends for various MPW tools, as well as deeper support for compilation and other kinds of file processing with MPW tools in third-party development systems.

Ultimately, MPW's command-line interface is destined to become a fading memory. Although it confers some advantages in power, it must give way to friendlier approaches in the end. However, if we fail to move its toolset forward into the post-command-line world, we will be poorer for the loss.

TIM MARONEY was discovered on the Isle of Wight by seal farmers in the Year of Our Lord 1394, and again seventy years later by Tasmanian basket twirlers out for a stroll in the Yukon. The little tyke pursued a happy life of fun, freedom, and quantum mechanics. He resurfaced in 1961, in the town of Holyoke, Massachusetts. Tim played a magician in bondage in a class play in the second grade, which may have prepared him for the contract work he's now doing at Apple.

Thanks to Deeje Cooley, Arno Gourdol, and Rick Mann for reviewing this column.

 
AAPL
$102.57
Apple Inc.
+0.32
MSFT
$45.09
Microsoft Corpora
+0.21
GOOG
$570.78
Google Inc.
+1.58

MacTech Search:
Community Search:

Software Updates via MacUpdate

VueScan 9.4.41 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Cloud 3.0.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more
LibreOffice 4.3.1.2 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
SlingPlayer Plugin 3.3.20.505 - Browser...
SlingPlayer is the screen interface software that works hand-in-hand with the hardware inside the Slingbox to make your TV viewing experience just like that at home. It features an array of... Read more
Get Lyrical 3.8 - Auto-magically adds ly...
Get Lyrical auto-magically add lyrics to songs in iTunes. You can choose either a selection of tracks, or the current track. Or turn on "Active Tagging" to get lyrics for songs as you play them.... Read more
Viber 4.2.2 - Send messages and make cal...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device,... Read more
Cocktail 7.6 - General maintenance and o...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
LaunchBar 6.1 - Powerful file/URL/email...
LaunchBar is an award-winning productivity utility that offers an amazingly intuitive and efficient way to search and access any kind of information stored on your computer or on the Web. It provides... Read more
Maya 2015 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more
BBEdit 10.5.12 - Powerful text and HTML...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more

Latest Forum Discussions

See All

The Walking Dead Pinball Review
The Walking Dead Pinball Review By Blake Grundman on August 29th, 2014 Our Rating: :: DECISIONS, DECISIONS...Universal App - Designed for iPhone and iPad Zen Studios is at it again, taking a property that would never seem to work... | Read more »
Stupeflix Has Released a Major Update fo...
Stupeflix Has Released a Major Update for Replay Posted by Jessica Fisher on August 29th, 2014 [ permalink ] iPhone App - Designed for the iPhone, compatible with the iPad | Read more »
ALONE… Review
ALONE… Review By Jennifer Allen on August 29th, 2014 Our Rating: :: MINIMALISTIC AND TOUGHUniversal App - Designed for iPhone and iPad Tough yet satisfying, ALONE… is a challenging endless flyer with some suitably sensitive... | Read more »
Hyperlapse Review
Hyperlapse Review By Jennifer Allen on August 28th, 2014 Our Rating: :: SPEEDY VIDEO SNAPSUniversal App - Designed for iPhone and iPad Want to make a great time-lapse video quickly? Hyperlapse is perfect for that.   | Read more »
Back To Bed Review
Back To Bed Review By Jennifer Allen on August 28th, 2014 Our Rating: :: STYLISH BUT LIMITEDUniversal App - Designed for iPhone and iPad It looks gorgeous, but Back to Bed is actually a fairly simple and uneventful puzzle game.   | Read more »
New Cars, New Locations, and a New Seaso...
New Cars, New Locations, and a New Season in Asphalt 8: Airborne Update Posted by Jessica Fisher on August 28th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Award Winning Children’s Book Bedtime fo...
Bedtime for Sarah Sullivan is a children’s storybook that emphasizes the importance of going to bed, dreams, and those magical moments right before being tucked in. Now Kelly Paniagua, author of the award-winning children’s book, is planning to... | Read more »
Happy Cube Death Arena Review
Happy Cube Death Arena Review By Jordan Minor on August 28th, 2014 Our Rating: :: CUBEDUniversal App - Designed for iPhone and iPad Happy Cube Death Arena is adorably violent, but very, very shallow.   | Read more »
8bit Doves, the New Game from Icebreaker...
8bit Doves, the New Game from Icebreaker Developers Nitrome, is Now Available – and in Four Colours Posted by Ellis Spice on August 28th, 2014 [ | Read more »
Ace Ferrara and the Dino Menace Review
Ace Ferrara and the Dino Menace Review By Nadia Oxford on August 28th, 2014 Our Rating: :: DINO-MYTEUniversal App - Designed for iPhone and iPad Ace Ferrara and the Dino Menace combines space combat and weird humor into a fun game... | Read more »

Price Scanner via MacPrices.net

New 21″ 1.4GHz iMac on sale again for $999, s...
Best Buy has the new 21″ 1.4GHz iMac on sale for $999.99 on their online store. Their price is $100 off MSRP. Choose free shipping or free local store pick up. Price is for online orders only, in-... Read more
Smartphone Outlook Remains Strong for 2014, U...
According to a new mobile phone forecast from the International Data Corporation (IDC) Worldwide Quarterly Mobile Phone Tracker, more than 1.25 billion smartphones will be shipped worldwide in 2014,... Read more
Save up to $60 with Apple refurbished iPod to...
The Apple Store has Apple Certified Refurbished 5th generation iPod touches available starting at $149. Apple’s one-year warranty is included with each model, and shipping is free. Many, but not all... Read more
12-Inch MacBook Air Coming in 4Q14 or 2015 –...
Digitimes’ Aaron Lee and Joseph Tsai report that according to Taiwan-based upstream supply chain insiders, Apple plans to launch a thinner MacBook model either at year end 2014 or in 2015, and that... Read more
Sapphire Screen “Most Wanted” iPhone 6 New Fe...
According to the ‘uSell.com iPhone Most Wanted Survey’ — a representative survey of 1,000 U.S. smartphone users conducted by used iPhone marketplace uSell.com — close to half of all smartphone users... Read more
The iPad’s Real Competitive Challenger (Not S...
It’s been my contention for some time that the iPad is suffering from something of an identity crisis, and I suspect that may be a factor in slackening sales this year. Apple can’t seem to decide... Read more
13-inch 2.6GHz/256GB Retina MacBook Pro on sa...
B&H Photo has the 13″ 2.6GHz/256GB Retina MacBook Pro on sale for $1379 including free shipping plus NY sales tax only. Their price is $120 off MSRP. Read more
Life Inventory iOS Apps – Learn to Know Thyse...
James Hollender’s Life Inventory apps s are now on sale with 20% off thru Labor Day, 09/01/2014. This is a great opportunity to get started on that Moral Inventory you’ve been putting off doing for... Read more
Pocket Watch, LLC. Reveals Cloud Server For P...
Beaumont, Texas based Pocket Watch, LLC. has announced the availability of its new ActivePrint Cloud Server Powered by Raspberry Pi. With this small standalone box almost any USB printer or available... Read more
902it Simplifies Area Code Changes For Nova S...
The east coast Canadian provinces of Nova Scotia and Prince Edward Island are phasing in 10 digit telephone dialing, to be fully in place by November, in order to accommodate a second area code to... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.