create_postgis.sh

#!/usr/bin/env bash
POSTGIS_SQL_PATH=`pg_config --sharedir`/contrib/postgis-2.1
createdb -E UTF8 template_postgis # Create the template spatial database.
createlang -d template_postgis plpgsql # Adding PLPGSQL language support.
psql -d postgres -c "UPDATE pg_database SET datistemplate='true' WHERE datname='template_postgis';"
psql -d template_postgis -f $POSTGIS_SQL_PATH/postgis.sql # Loading the PostGIS SQL routines
psql -d template_postgis -f $POSTGIS_SQL_PATH/spatial_ref_sys.sql
psql -d template_postgis -c "GRANT ALL ON geometry_columns TO PUBLIC;" # Enabling users to alter spatial tables.
psql -d template_postgis -c "GRANT ALL ON geography_columns TO PUBLIC;"
psql -d template_postgis -c "GRANT ALL ON spatial_ref_sys TO PUBLIC;"

this work on OSX after you get all the pieces installed. Start by deleting the homebrew installations of postgres and postgis then running this as the _postgres user.