To have scripted automated backup of PostgreSQL databases on a linux platform, you can create a script like so:

#!/bin/bash
PGPASSWORD="your-password" /usr/bin/pg_dump -U user database > sql-file.sql

Replace user and your-password with your username and password; replace database with the database you want to backup. The output of the dump goes to stdout and can be piped to a plain text file or compressed to something else.