go install github.com/fiatjaf/eventstore/cmd/eventstore@latest

This should be pretty straightforward. You pipe events or filters, as JSON, to the eventstore command, and they yield something. You can use nak to generate these events or filters easily.

~> nak req -k 1 -l 100 --bare | eventstore -d /path/to/store query
~> # or
~> echo '{"kinds":[1],"limit":100}' | eventstore -d /path/to/store query

This will automatically determine the storage type being used at /path/to/store, but you can also specify it manually using the -t option (-t lmdb, -t sqlite etc).

~> nak event -k 1 -c hello | eventstore -d /path/to/store put
~> # or
~> echo '{"id":"35369e6bae5f77c4e1745c2eb5db84c4493e87f6e449aee62a261bbc1fea2788","pubkey":"79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798","created_at":1701193836,"kind":1,"tags":[],"content":"hello","sig":"ef08d559e042d9af4cdc3328a064f737603d86ec4f929f193d5a3ce9ea22a3fb8afc1923ee3c3742fd01856065352c5632e91f633528c80e9c5711fa1266824c"}' | eventstore -d /path/to/store put

You can also create a database from scratch if it's a disk database, but then you have to specify -t to sqlite, badger or lmdb.

You should be able to connect by just passing the database connection URI to -d:

~> eventstore -d 'postgres://myrelay:38yg4o83yf48a3s7g@localhost:5432/myrelay?sslmode=disable' <query|put|del>

That should be prefixed with postgres:// for Postgres, mysql:// for MySQL and https:// for ElasticSearch.