Export without typing password

Sometimes cronjobs help us to automate routine tasks like export.
But these text based script files can include passwords which is an uncool sutiation.
One solution is to add cronjobs to dba groups' users crontabs. guess what :-) oracle
Here is an example without typing passwords.

exp \'/ as sysdba\' full=y direct=y file=fullnopwd.dmp log=fullnopwd.log