This does not directly address your question, but I can suggest that, since the bodies of your loops seem very similar if not identical, there is a way to more concisely express the requirement to loop through all passwords from '0000' to '9999' using the sprintf built-in.

>perl -wMstrict -e
"for (0 .. 2, 103 .. 105, 9997 .. 9999) {
   my $password = sprintf qq{%04d}, $_;
   print qq{$password }
   }
"
0000 0001 0002 0103 0104 0105 9997 9998 9999
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You may also, in future, wish to consider enclosing large chunks of code in <readmore> ... </readmore> tags; please see Writeup Formatting Tips for more info. (You can even update your post to do this now!)

Update:   It's also a good idea to check the return status of any file or network I/O operations and die or warn as appropriate.