If it is a simple shell script, then you don't need to wrap it in an application bundle; you can double-click the script itself. However, you won't get the ability to have a custom icon or other things like that.

I think there are a few helpers out there that can wrap simple scripts, but the only one that I have experience with is [Platypus][1] which allows you to make shell/python/perl/ruby/etc scripts run like regular applications with icons, I/O redirections, etc.

Where Platypus differs here is that you CAN get STDIN / STDOUT through a few different mechanisms, as well as menu bar interactivity. So you get a window where you can interact with whatever script is actually running.


  [1]: http://www.sveinbjorn.org/platypus