"Useful" self-modifying script for financial firm
Pseudocode

// Set up a cron job to run this script (only) once a day

yesterdays_stock_price = '46.48'

todays_stock_price = curl_google_finance('VTSMX')

print "Difference between yesterday's stock price and today's: "

print todays_stock_price

self = open('self.file')

self.replace( /yesterdays_stock_price = '[0-9\.]+'/, todays_stock_price)

self.save()