Is it a Diff or not? Your program will be run an undetermined amount of times. On all but the last, there will be a file called data in the same directory of your program that has the same value each time. On the last run, the file will be there but will have different data in it. On all the times except the last, you can do whatever you want, as long as the following rules are met:


Don't output anything
Don't change data file


On the last run, you must print out the diff of the first data file and the current data file.

Rules:


You may save whatever you want in any files you want, just don't edit the data file


Scoring:


Lowest char score wins


Cheating encouraged. You have no indication of which run you're in except that the data file is changed.
Bash (31)

[ -e x ]&amp;&amp;diff data x;cp data x


Kinda obvious.