Very cool idea. I've got update notification in framechat and reputer that merely compares the script version with info in an html comment somewhere on perlmonks when a certain button is selected.

To update in-place I would try to separate code that's subject to updates into a file to require, so the #! and any user defined vars are left intact. I'd also be concerned with portable methods of creating and executing new files.

Looking forward to whatever you come up with.

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Check out my Perlmonks Related Scripts like framechat, reputer, and xNN.