In the following article you will find a few basic command for backups on PostgreSQL databases.

You can simply dump a database into a SQL file by using pg_dump

pg_dump db_name > /var/backups/db_name.sql

If you want to compress the output you can pipe the stream to gzip and the save it in a file:

pg_dump db_name | gzip > /var/backups/db_name.sql.gz