Two comments:

1. Check the return values of close calls as well as open. You'll probably also want to print $! in the message.
2. I always keep system files in an RCS repository. This has saved my butt only once, but when it did, I was most grateful. You could use the Rcs module, but it's probably overkill; something like

    system("ci -l -m 'adding user $username\@$domain' $datafile") == 0
      or die "RCS check-in of $datafile failed: $?\n";
   [download]

   should suffice. (Note: haven't tested the error checking; I just pulled that out of perldoc -f system.)

--
F o x t r o t U n i f o r m
Found a typo in this node? /msg me
The hell with paco, vote for Erudil!