How to Use LSET Command in Redis to Update List Elements

The LSET command in Redis updates the element at a specific index in a list stored at a key. Use LSET key index value to replace the element at index with value. The index can be positive (from start) or negative (from end).

Syntax

The LSET command updates an element in a Redis list at a given index.

• key: The name of the list.
• index: Position of the element to update (0-based, negative counts from the end).
• value: New value to set at the specified index.

If the index is out of range, Redis returns an error.

redis

LSET key index value

Example

This example shows how to update the second element (index 1) in a list called fruits from "banana" to "blueberry".

redis

127.0.0.1:6379> RPUSH fruits apple banana cherry
(integer) 3
127.0.0.1:6379> LRANGE fruits 0 -1
1) "apple"
2) "banana"
3) "cherry"
127.0.0.1:6379> LSET fruits 1 blueberry
OK
127.0.0.1:6379> LRANGE fruits 0 -1
1) "apple"
2) "blueberry"
3) "cherry"

Output

1) "apple"
2) "banana"
3) "cherry"
OK
1) "apple"
2) "blueberry"
3) "cherry"

Common Pitfalls

Common mistakes when using LSET include:

• Using an index that is out of range, which causes an error.
• Trying to use LSET on a key that does not hold a list.
• Confusing zero-based indexing with one-based indexing.

Always check the list length with LLEN before using LSET to avoid errors.

redis

127.0.0.1:6379> LSET fruits 5 mango
(error) ERR index out of range

127.0.0.1:6379> SET notalist value
OK
127.0.0.1:6379> LSET notalist 0 something
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Output

(error) ERR index out of range
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Quick Reference

Command	Description
LSET key index value	Set list element at index to value
LLEN key	Get length of the list
LRANGE key start stop	Get elements in a range
RPUSH key value	Add element to the end of the list

Key Takeaways

Use LSET to update an element at a specific index in a Redis list.

Indexes are zero-based; negative indexes count from the end of the list.

LSET returns an error if the index is out of range or the key is not a list.

Check list length with LLEN before using LSET to avoid errors.

LSET modifies the list in place without changing its length.