Command
psql -U username dbname < backup.sql
Explanation
Restores a PostgreSQL database from a SQL dump file.
Examples
Restore database from file
psql -U postgres mydb < mydb_backup.sql
psql -U username dbname < backup.sql
Restores a PostgreSQL database from a SQL dump file.
Restore database from file
psql -U postgres mydb < mydb_backup.sql