Returns the remaining time to live of a key that has a timeout. This introspection capability allows a Redis client to check how many seconds a given key will continue to be part of the dataset.
In Redis 2.6 or older the command returns -1 if the key does not exist or if the key exist but has no associated expire.
Starting with Redis 2.8 the return value in case of error changed:The command returns -2 if the key does not exist. The command returns -1 if the key exists but has no associated expire.
See also the PTTL command that returns the same information with milliseconds resolution (Only available in Redis 2.6 or greater).
Integer reply: TTL in seconds, or a negative value in order to signal an error (see the description above).
redis> SET mykey "Hello""OK"
redis> EXPIRE mykey 10(integer) 1
redis> TTL mykey(integer) 10 redis>