The tool that we are creating for Redis will support three commands:

• add - adds a new session record
• remove - removes a session record by key (that is, by username)
• list - prints all session records

We need constants for the name of every subcommand to prevent mistakes in strings in the code:

const SESSIONS: &str = "sessions";
const CMD_ADD: &str = "add";
const CMD_REMOVE: &str = "remove";
const CMD_LIST: &str = "list";

This list also contains the SESSION constant as the name of the HashMap in Redis. Now, we can declare functions to manipulate session data.