This is a handy script for temporarily running postgresql while you execute a command: the DB is started against the specified data directory (which must already exist), then the command is run, and finally the DB is stopped again.
The DB listens only on a domain socket, and appropriate values of the
standard PG* environment variables are set while running the
specified command such that it will use that connection.
In conjunction with Nix, for example, this can be used to access data from old DB installations, e.g.
nix-shell -p postgresql_9_6 --run "./with-temp-postgres /usr/local/var/postgres-9.6 psql -l"