On Mac OS X, some applications will display a notification that appears briefly in the upper-right corner (e.g., when I receive email).

Is there a way to generate a notification from the command-line? In other words, is there a command-line program I can run to display a custom notification, with text of my choice? Ideally, I'd love to be able to run something like

 show-notification "Hello world!"

from a shell script and have a notification appear showing the text "Hello world!".

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I discovered I can use [this answer](http://apple.stackexchange.com/a/83359/24154) to display a dialog box in the center of the screen that the user has to click "OK" on, but I'm looking for a notification not a modal dialog box.