system("$oracle_home/bin/sqlldr $user_id/$user_pwd@$sid
   control=$oracle_base/scripts/sqlldr/$ctlfile 
   errors=$errors log=$oracle_base/scripts/sqlldr/$logfile
   >/dev/null 2>&1");
[download]

should be

system("$oracle_home/bin/sqlldr $user_id/$user_pwd\@$sid
   control=$oracle_base/scripts/sqlldr/$ctlfile 
   errors=$errors log=$oracle_base/scripts/sqlldr/$logfile
   >/dev/null 2>&1");
[download]

The backslash in front of the @ is necessary to prevent interpolation errors (weird that -w isn't picking this up).

update nor does 'use warnings' but 'use strict' will.