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:
If this was an SQL backup file, this should have failed with:
pg_restore: error: input file appears to be a text format dump. Please use psql.
pg_restore does not accept SQL backup files as input. It accepts the custom backup format, is that what you used?
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?
pg_restore with --create and --clean would drop and recreate whatever database was named inside the custom dump file. The argument to --dbname is only used as the database to connect to in order to do this drop and create of the one named inside the dump file. So this should not have overwritten the "postgres" database. (Unless that was the database which was dumped, and since you can't drop the database you are connected to, that shouldn't have worked anyway)
The "postgres" database is usually just used for administrative tasks, and has no interesting contents. If you did somehow manage to overwrite it, you might not have to do anything.