pg_dump + cronjob

Hi list,
i've written a script for dumping several databases (mysql + PG), and it
runs fine. But now i have the problem to convert it into a cron script.
how can i run pg_dump with password? i found nothing in the manpages
about pg login and passwords, e.g. on mysql i can use --password=xxx.
any ideas how todo this?

Greetings,
Gerd
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