Why does Postgres dropdb works but psql DROP DATABASE doesn't?

Question

I am writing a script that will drop PostgreSQL database. I do it like this:

echo "> Prevent connection of new users."
PGPASSWORD=$PG_PASSWORD_IMPORT psql \
    -h $PG_HOST_IMPORT -p $PG_PORT_IMPORT -U $PG_USER_IMPORT -d $PG_DATABASE_IMPORT \ 
    -c "REVOKE CONNECT ON DATABASE $PG_DATABASE_IMPORT FROM PUBLIC, $PG_USER_IMPORT;"

echo "> Terminate existing connections."
PGPASSWORD=$PG_PASSWORD_IMPORT psql \
    -h $PG_HOST_IMPORT -p $PG_PORT_IMPORT -U $PG_USER_IMPORT -d $PG_DATABASE_IMPORT \
    -c "SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE pid <> pg_backend_pid() AND datname = '$PG_DATABASE_IMPORT';"

echo "> Drop '$PG_DATABASE_IMPORT' database."
PGPASSWORD=$PG_PASSWORD_IMPORT dropdb \
    -h $PG_HOST_IMPORT -p $PG_PORT_IMPORT -U $PG_USER_IMPORT  $PG_DATABASE_IMPORT

and it works well.

But when I try to drop database using psql, then I get error ERROR: cannot drop the currently open database.

echo "> Prevent connection of new users."
PGPASSWORD=$PG_PASSWORD_IMPORT psql \
    -h $PG_HOST_IMPORT -p $PG_PORT_IMPORT -U $PG_USER_IMPORT -d $PG_DATABASE_IMPORT \
    -c "REVOKE CONNECT ON DATABASE $PG_DATABASE_IMPORT FROM PUBLIC, $PG_USER_IMPORT;"

echo "> Terminate existing connections."
PGPASSWORD=$PG_PASSWORD_IMPORT psql \
    -h $PG_HOST_IMPORT -p $PG_PORT_IMPORT -U $PG_USER_IMPORT -d $PG_DATABASE_IMPORT \
    -c "SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE pid <> pg_backend_pid() AND datname = '$PG_DATABASE_IMPORT';"

echo "> Drop '$PG_DATABASE_IMPORT' database."
PGPASSWORD=$PG_PASSWORD_IMPORT psql \
    -h $PG_HOST_IMPORT -p $PG_PORT_IMPORT -U $PG_USER_IMPORT -d $PG_DATABASE_IMPORT \
    -c "DROP DATABASE $PG_DATABASE_IMPORT;"

I find it strange, because according to the documentation, dropdb is a wrapper around the SQL command DROP DATABASE.

Answer 1

The dropdb documentation says:

--maintenance-db= dbname

Specifies the name of the database to connect to in order to drop the target database. If not specified, the postgres database will be used; if that does not exist (or is the database being dropped), template1 will be used.

dropdb connects to postgres , not to the database about to be dropped, that's why it works in this case.