----This My script content.
 --This will accept "Char" datatype as an Input and it will pront you when you execute the script as 'Please Enter start_date:'

Dev>host type e:\test.sql
undef start_date
accept start_date char prompt 'Please Enter start_date:'  
select to_date(&start_date,'yyyymmdd') from dual;

---Now I am calling that script from sqlplus

Dev>@ e:\test.sql
Please Enter start_date:20121010
old   1: select to_date(&start_date,'yyyymmdd') from dual
new   1: select to_date(20121010,'yyyymmdd') from dual

TO_DATE(2
---------
10-OCT-12

Dev>