Expiry and TTL

Key Expiry

One of Redis's killer features is built-in key expiration. You can set any key to automatically disappear after a given time. No cron jobs, no cleanup code — Redis handles it automatically.

SET with EX (seconds)

Set a key and its expiry in one command:

SET session "abc123" EX 3600

This key will expire in 3600 seconds (1 hour). Redis's lazy expiration removes expired keys when they are accessed.

EXPIRE — Set Expiry After the Fact

Add expiry to an existing key:

SET cache "some data"
EXPIRE cache 300

Returns (integer) 1 if the expiry was set, (integer) 0 if the key doesn't exist.

TTL — Time To Live

Check how many seconds remain before a key expires:

SET token "xyz" EX 60
TTL token

Output:

OK
(integer) 60

Return values:

• Positive integer: seconds until expiry
• -1: key exists but has no expiry
• -2: key does not exist

PEXPIRE and PTTL — Millisecond Precision

PEXPIRE key 5000    -- expire in 5000 milliseconds
PTTL key            -- remaining time in milliseconds

PERSIST — Remove Expiry

Turn a key with expiry into a permanent key:

SET temp "value" EX 60
PERSIST temp
TTL temp

Output:

OK
(integer) 1
(integer) -1

Common Patterns

Session tokens:

SET session:user123 "token_data" EX 86400

Cache with TTL:

SET cache:query:12345 "result_data" EX 300

One-time codes:

SET otp:user@example.com "482910" EX 300

Your Task

Set a key api_key to "secret123" with a 60-second expiry. Then check its TTL.