Recently I needed to create a duplicate of PGSQL database.  Being a MySQL guy, I didn’t know off hand how to do it, but here is an easy way:

pg_dump original_db > original_db.sql
createdb new_db
psql -d new_db < original_db.sql

From a bird’s eye view, you are creating a dump of the original database and outputting it to a file. From there, make sure the new database is created and use your dump file as input for that database. It wouldn’t be too hard to make this into a one-liner, but I like to see intermediate steps to make sure things are going well.