Re: overwrote THE 'postgres' database - how to recover

I was experimenting with creating a copy of an existing database from
a pg_dump sql backup file.  I made an misake in failing to delimit an
environment variable and in consequence I issued this command as user
postgres:

I should have used:

gunzip < "$APP_DBNAME".pgsql.gz | pg_restore --create --clean
--user=postgres --dbname="$APP_DBNAME"_copy  &&  vacuumdb
--user=postgres --full --analyze "$APP_DBNAME"_copy

But, instead I did this:

gunzip < $APP_DBNAME.pgsql.gz | pg_restore --create --clean
--user=postgres --dbname=$APP_DBNAME_copy  &&  vacuumdb
--user=postgres --full --analyze $APP_DBNAME_copy

which resulted in this:

gunzip < hll_redmine.pgsql.gz  |  pg_restore --create --clean
--user=postgres --dbname=  &&  vacuumdb --user=postgres --full
--analyze

Which caused the postgres database to be overwritten with
hll_redmine.pgsql.gz.  Is there an easy way to get this back or do I
have to reinitialise the whole thing?