Like I said in my first reply, I like to check md5sums. If you want to only call a save routine, if a modification is made, you have those 2 options. One, if the editModified flag is 1, call a save routine upon exiting. Or you can do a get('0.0','end') on loading the file, and do an md5sum on the string and store it away. Then have something like this in you code:

$SIG{__DIE__} = sub {&save_it(); exit};
$SIG{INT} = sub {&save_it(); exit};

#have your exit button call &save_it too

sub save_it{

# do another get('0.0','end') 
# take an md5sum of the text and compare
# it to your original md5sum
# save your text if they differ

}
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Otherwise you will be auto-saving on every keystroke. You can also work out an auto-save scheme if the text box goes out of focus.