Backup: http://www.postgresql.org/docs/current/static/app-pgdump.htm...

In short:

  pg_dump -Fc mydb > db.dump

Restore: http://www.postgresql.org/docs/current/static/app-pgrestore....

In short:

  pg_restore -C -d postgres db.dump

Command directly from the shell:

  psql -c "psql command"