Date::Manip has all you need. Here is an untested sketch of why:

use Date::Manip;
my $err;
for ( my $mydate = '2005-07-12', my $theirdate = ParseDate($mydate);
 $mydate le '2005-08-03';
 $theirdate = DateCalc( $theirdate, '+ 1days', \$err ) or die $err )
 {
   $mydate = &UnixDate( $theirdate,"%y%-%m%-%d");
   # now $mydate is ready for use in this loop
}
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