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Wednesday, November 19, 2008

Wrapping Scripts with Platypus on Mac OS X

Platypus is a Mac OS X tool, written by Sveinbjorn Thordarson, that lets you create Mac OS X applications that wrap up command line scripts, create installers, etc. It is a great way to package Ruby, Perl, etc. scripts for a broader user audience.

Platypus is easy to figure out if you just have a single script. But I often times develop data analysis pipelines of various sorts where I have one master Ruby script calling a bunch of others.

Wrapping the whole thing up with Platypus can work really well but to do that you need to understand how the tool works.

At first glance you might think that it just calls the target script in its original location, but in fact it copies the script into the folder that embodies the Mac OS X application. So if I have a primary script calling a secondary one then I need to either refer to it by an absolute path, which is not a good idea for portability, or I need to include the secondary script in the Mac application.

Here is an example that shows how you handle this - I'll assume that you have tried Platypus with some simple scripts already.

The primary script (hello.rb) is what the Platypus generated application will execute. This in turn will execute world.rb and echo its output.


puts "Hello ..."
world = File.join(File.dirname(__FILE__), 'world.rb')
puts `#{world}`


puts "... World"

First of all, specify the path to your Ruby (or whatever) interpreter explicitly. The convention in the Ruby world is to use '#!/usr/bin/env ruby' but doesn't work directly with Platypus. I'm sure you can mess with some of the Platypus options to make it work but I haven't bothered.

The third line in hello.rb specifies where to find the script 'world.rb', namely in the same directory as hello.rb. For Perl coders, this is the same as using FindBin.

Package hello.rb with Platypus, sending output to a Text window and keeping the window open after the script completes, then run the script. You should get something like this:

/Users/jones/Documents/Platypus/hello_world.app/Contents/Resources/script:7: command not found: /Users/jones/Documents/Platypus/hello_world.app/Contents/Resources/world.rb
Hello ...

It has found and run hello.rb but it can't find world.rb. The error message tells us that the script it has run is actually called 'script', not hello.rb, which seems odd.

Platypus copies your script into a new Mac application, which as you should know, is really a directory. 'cd' to the application directory (hello_world.app in my case), then into Contents -> Resources.

Look at the file 'script' and you'll see that is actually 'hello.rb'

To get the result you want you have to add 'world.rb' to the application as a 'Resource' and you do this in the 'Advanced Options' panel in Platypus. Just add the secondary file to this panel, rebuild the application and re-run it.

Hello ...
... World

With more complex applications you can add additional scripts and data files. Test things out by running them from the command line in the platypus generated application directory.

If you want to get around this you can specify an absolute path to the secondary script, or create a symlink to it from within the application directory. But down this path lies madness. A better alternative would be to use an environment variable to show where something lies, such as the PATH variable or something custom. Platypus will let you pass that into the app.

I'm very impressed with Platypus, compared to earlier attempts at doing this, like DropScript. When I get the chance I want to try it in combination with CocoaDialog which allows you to create simple GUIs in your scripts.

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