Export POSTGRES_USER and POSTGRES_DB vars in entrypoint

[md5]

As it now stands the $POSTGRES_USER and $POSTGRES_DB variables aren't visible in /docker-entrypoint-initdb.d/*.sh scripts unless they have been set explicitly with -e in the docker run command or with ENV in a derived Dockerfile.

This change allows those variables to be seen in the *.sh scripts. Without this change, any *.sh scripts that want to follow the same conventions as the postgres base image need to duplicate this code:

: ${POSTGRES_USER:=postgres} : ${POSTGRES_DB:=$POSTGRES_USER}

I ran into this while trying to implement postgis/docker-postgis#4 (Enable PostGIS extensions on default database).

[tianon]

Good call; LGTM 👍

[yosifkit]

LGTM