Optional blockingOptional dataUsed for "database" commands to enforce type checking.
Private loggerMaximum number of parameters allowed. -1 for no maximum.
Minimum number of parameters require.
Optional pubUsed when PUB/SUB is in effect.
Optional signSign is used in commands with a compliment command. The only current example is INCR/DECR. Sign is 1 for INCR and -1 for DECR
Optional txUsed in transactions to enqueue a command.
Every command must implement the execute method.
Available since v1.0.0
EXISTS key [key...] Returns if key exists.
Since Redis 3.0.3 it is possible to specify multiple keys instead of a single one. In such a case, it returns the total number of keys existing. Note that returning 1 or 0 for a single key is just a special case of the variadic usage, so the command is completely backward compatible.
The user should be aware that if the same existing key is mentioned in the arguments multiple times, it will be counted multiple times. So if somekey exists, EXISTS somekey somekey will return 2.
Return value Integer reply, specifically:
1 if the key exists. 0 if the key does not exist. Since Redis 3.0.3 the command accepts a variable number of keys and the return value is generalized:
The number of keys existing among the ones specified as arguments. Keys mentioned multiple times and existing are counted multiple times.