$ tar xfj ..../postgresql/src.tar.bz2
  # create a directory postgresql-12.1
$ source your/environment/file
  # set up environment variables
$ configure --prefix=$PGHOME
$ make
$ make install
$ initdb
  # set up postgresql configuration ... done once?
$ edit postgresql.conf
$ pg_ctl start -l $PGDATA/log
  # do some work with PostgreSQL databases
$ pg_ctl stop