Autopex is PostgreSQL extension installation magic. It ties together Pex with event triggers to automatically download and build extensions that you want to install.
Install Autopex like a normal extension:
$ make PG_CONFIG=/some/where/pg_config install
$ psql dbname
=# CREATE EXTENSION autopex;
Also install Pex and run pex init under the PostgreSQL user account (probably postgres).
Then you can create any extension, such as
=# CREATE EXTENSION plsh;
=# CREATE EXTENSION prefix;
and they will automatically be downloaded and built before the actual CREATE EXTENSION command runs.
PostgreSQL 9.3 or later is required.