Redis
Redis is an in-memory key-value database. See also: NoSQL.
$ sudo apt install redis-tools
By default, it runs on port 6379
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$ redis-cli [-h host] [-p port]
host:port> help # list commands
host:port> info # get information
host:port> keys * # list keys
host:port> get some_key # get some value
host:port> set key value # set some value
host:port> del key # delete a key