# BLMOVEM ```json metadata { "title": "BLMOVEM", "description": "Moves up to (or exactly) a number of elements from one list to another and returns them. Blocks until the elements are available otherwise. Deletes the source list if it becomes empty.", "categories": ["docs","develop","stack","oss","rs","rc","oss","kubernetes","clients"], "arguments": [{"display_text":"source","key_spec_index":0,"name":"source","type":"key"},{"display_text":"destination","key_spec_index":1,"name":"destination","type":"key"},{"arguments":[{"display_text":"left","name":"left","token":"LEFT","type":"pure-token"},{"display_text":"right","name":"right","token":"RIGHT","type":"pure-token"}],"name":"wherefrom","type":"oneof"},{"arguments":[{"display_text":"left","name":"left","token":"LEFT","type":"pure-token"},{"display_text":"right","name":"right","token":"RIGHT","type":"pure-token"}],"name":"whereto","type":"oneof"},{"display_text":"timeout","name":"timeout","type":"double"},{"arguments":[{"arguments":[{"display_text":"count","name":"count","token":"COUNT","type":"integer"},{"display_text":"exactly","name":"exactly","token":"EXACTLY","type":"integer"}],"name":"selector","type":"oneof"},{"arguments":[{"display_text":"obo","name":"obo","token":"OBO","type":"pure-token"},{"display_text":"bulk","name":"bulk","token":"BULK","type":"pure-token"}],"name":"ordering","type":"oneof"}],"name":"how-many","optional":true,"type":"block"}], "syntax_fmt": "BLMOVEM source destination \u003cLEFT | RIGHT\u003e \u003cLEFT | RIGHT\u003e timeout\n [\u003cCOUNT count | EXACTLY exactly\u003e \u003cOBO | BULK\u003e]", "complexity": "O(N) where N is the number of elements moved.", "group": "list", "command_flags": ["write","denyoom","blocking"], "acl_categories": ["@write","@list","@slow","@blocking"], "since": "8.10.0", "arity": -6, "key_specs": [{"RW":true,"access":true,"begin_search":{"spec":{"index":1},"type":"index"},"delete":true,"find_keys":{"spec":{"keystep":1,"lastkey":0,"limit":0},"type":"range"}},{"RW":true,"begin_search":{"spec":{"index":2},"type":"index"},"find_keys":{"spec":{"keystep":1,"lastkey":0,"limit":0},"type":"range"},"insert":true}], "tableOfContents": {"sections":[{"id":"required-arguments","title":"Required arguments"},{"id":"optional-arguments","title":"Optional arguments"},{"children":[{"id":"blocking-behavior","title":"Blocking behavior"}],"id":"details","title":"Details"},{"id":"redis-software-and-redis-cloud-compatibility","title":"Redis Software and Redis Cloud compatibility"},{"id":"return-information","title":"Return information"},{"id":"see-also","title":"See also"},{"id":"related-topics","title":"Related topics"}]} , "codeExamples": [] } ``` This command's behavior varies in clustered Redis environments. See the [multi-key operations](https://redis.io/docs/latest/develop/using-commands/multi-key-operations) page for more information. `BLMOVEM` is the blocking variant of [`LMOVEM`](https://redis.io/docs/latest/commands/lmovem). When `source` holds enough elements to satisfy the request, this command behaves exactly like [`LMOVEM`](https://redis.io/docs/latest/commands/lmovem). Otherwise, Redis blocks the connection until another client pushes the required elements to `source` or until `timeout` is reached. ## Required arguments
source The key of the source list.
destination The key of the destination list.
LEFT | RIGHT The end of `source` to pop elements from: `LEFT` (head) or `RIGHT` (tail).
LEFT | RIGHT The end of `destination` to push elements to: `LEFT` (head) or `RIGHT` (tail).
timeout The maximum time to block, in seconds. A timeout of `0` blocks indefinitely.
## Optional arguments The `how-many` block controls how many elements are moved and in what order. When you include it, you must provide both a selector (`COUNT` or `EXACTLY`) and an ordering (`OBO` or `BULK`).
COUNT count | EXACTLY exactly The number of elements to move: - `COUNT count` moves up to `count` elements. If `source` holds fewer than `count` elements, all of them are moved. This matches the `count` semantics of [`LPOP`](https://redis.io/docs/latest/commands/lpop) and [`LMPOP`](https://redis.io/docs/latest/commands/lmpop). - `EXACTLY exactly` moves exactly `exactly` elements. If `source` holds fewer than `exactly` elements, the command blocks (see [Blocking behavior](#blocking-behavior)).
OBO | BULK The order in which elements are pushed onto `destination`: - `OBO` (one by one) moves elements individually: each element is popped from `source` and pushed to `destination` before the next one is moved. - `BULK` moves all of the elements at once, preserving their relative order. See the [Element ordering](https://redis.io/docs/latest/commands/lmovem#element-ordering) section of the [`LMOVEM`](https://redis.io/docs/latest/commands/lmovem) documentation for details.
## Details ### Blocking behavior Whether `BLMOVEM` blocks depends on the selector: - With `COUNT`, the command blocks only while `source` is empty. As soon as at least one element is available it unblocks, moves up to `count` elements, and returns them. - With `EXACTLY`, the command blocks while `source` holds fewer than the requested number of elements. It unblocks only once `source` grows to at least that length, then moves exactly that many elements atomically. A `timeout` of `0` blocks indefinitely. When used inside a [`MULTI`](https://redis.io/docs/latest/commands/multi)/[`EXEC`](https://redis.io/docs/latest/commands/exec) block or a Lua script, `BLMOVEM` does not block; it behaves like [`LMOVEM`](https://redis.io/docs/latest/commands/lmovem) and, when the request cannot be satisfied, returns nil immediately. ## Redis Software and Redis Cloud compatibility | Redis
Software | Redis
Cloud | Notes | |:----------------------|:-----------------|:------| | ❌ Standard
❌ Active-Active | ❌ Standard
❌ Active-Active | | ## Return information **RESP2:** One of the following: * [Array reply](../../develop/reference/protocol-spec#arrays): the moved elements, in destination order. * [Nil reply](../../develop/reference/protocol-spec#bulk-strings): the operation timed out. **RESP3:** One of the following: * [Array reply](../../develop/reference/protocol-spec#arrays): the moved elements, in destination order. * [Null reply](../../develop/reference/protocol-spec#nulls): the operation timed out. ## See also [`BLMOVE`](https://redis.io/docs/latest/commands/blmove/) | [`LMOVEM`](https://redis.io/docs/latest/commands/lmovem/) | [`BLMPOP`](https://redis.io/docs/latest/commands/blmpop/) | [`BRPOPLPUSH`](https://redis.io/docs/latest/commands/brpoplpush/) ## Related topics - [Redis lists](https://redis.io/docs/latest/develop/data-types/lists)