Multi tool use

Delete all entries in a Redis list

Suppose you have a LIST datatype in Redis. How do you delete all its entries? I've tried this already:

LTRIM key 0 0
LTRIM key -1 0


Both of those leave the first element. This will leave all the elements:

LTRIM key 0 -1


I don't see a separate command to completely empty a list.

mylist

LTRIM mylist 1 -1

5 Answers
5

Delete the key, and that will clear all items. Not having the list at all is similar to not having any items in it. Redis will not throw any exceptions when you try to access a non-existent key.

DEL key


Here's some console logs.

may create extra overhead

You can remove all values in the List only if the List has more than one value

LTRIM key -1 0


Example:

redis 127.0.0.1:6379> RPUSH mylist four 1 3 1
(integer) 4
redis 127.0.0.1:6379> KEYS *
1) "newKey"
2) "firstHash"
3) "secondList"
4) "test4"
5) "firstList"
6) "mylist"
redis 127.0.0.1:6379> LTRIM mylist -1 0
OK
redis 127.0.0.1:6379> LRANGE mylist 0 -1
(empty list or set)
redis 127.0.0.1:6379> KEYS *
1) "newKey"
2) "firstHash"
3) "secondList"
4) "test4"
5) "firstList"


But if the List has one value only , you must use

DEL key


Am answering on my phone so can't actually format the answer well.

This might be a late response but am sticking it here just in case someone still needs that functionality.

Short answer

ltrim mylist 0 - (n+1)
where mylist is key and n is length of mylist.

Long answer

The way ltrim works is that, it takes two indices and return the elements that fall between them inclusive of the indices.

Ltrim list startIndex endIndex

Example assuming we have a redis list with key mylist containing 10 entries:

ltrim mylist 0 5
will trim the list to elements starting from index 0 through to index 5. And discard those that fall outside that range.

Fortunately redis list operations support negative indexing which proves extremely useful in some situations. Typically when you don't know the length of the list.

-1 refers to last element, - 2 penultimate element, etc. And (-n) is the first element.

Out of range indexes are not harmful. If the end index is greater than length of the list, redis treats it as equal to last index.

This is why ltrim mylist 0, -(n +1) clear the list. It does so because (-n) is equivalent to index 0. Adding 1 to it leaves no element within that range since that will be before the first element.

ltrim mylist 0 -99999

I tried this and it works for me. Just change myList for your list name and execute it

redis-cli KEYS "myList:*" | xargs redis-cli DEL



redis-cli KEYS "myList:*" | xargs redis-cli DEL


the accepted answer is wrong. suppose i have

redis 127.0.0.1:6379> KEYS *
1) "newKey"
2) "firstHash"
3) "secondList"
4) "test4"
5) "firstList"
6) "mylist"


to use ahmed's example, which is actually correct.
now, if i do:

DEL 'test4'


i end up with:

1) "newKey"
2) "firstHash"
3) "secondList"
4) "firstList"
5) "mylist"`


so, i did not remove all entries from the 'test4' list, i removed test4 itself. not the same thing. not at all. i have a little app where the list keys are hashes computed from several data(well, aren't they all?), those lists sometimes are cleared, but the semantics of a empty list and a non-existent list are very different.
so, no, i do not want to DEL 'myhashes', i want just to remove all entries.

beware, oh ye who wanders here.

The LPUSH command inserts a new element on the head, while RPUSH inserts a new element on the tail. A new list is created when one of this operations is performed against an empty key. Similarly the key is removed from the key space if a list operation will empty the list. These are very handy semantics since all the list commands will behave exactly like they were called with an empty list if called with a non-existing key as argument.

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