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A **List** in Redis is an **ordered collection of string values**, implemented as a **double-ended queue (a doubly linked list)**.
Every element is a Redis String, and insertion order is preserved.

### Main properties

- **Elements are stored in the order they were added.**
- Elements can be added and removed **from either end**, from the front or the back.
- **Duplicate values are allowed** (it's not a Set).
- It fits **queues, stacks, logs, action histories**, and temporary buffers.

### Example

```bash
LPUSH tasks "send the report"
RPUSH tasks "call with the client"
LRANGE tasks 0 -1
```

Result:

```javascript
1) "call with the client"
2) "send the report"
```

`LPUSH` adds to the front, `RPUSH` adds to the back.

### Main commands

| Command | Description |
|---|---|
| `LPUSH key value [value ...]` | add element(s) to the **front** of the list |
| `RPUSH key value [value ...]` | add element(s) to the **back** of the list |
| `LPOP key` | remove and return an element **from the front** |
| `RPOP key` | remove and return an element **from the back** |
| `LRANGE key start stop` | get a range of elements |
| `LLEN key` | get the list's length |
| `LINDEX key index` | get an element by index |
| `LREM key count value` | remove an element by value |
| `LTRIM key start stop` | trim the list to a range |

### A queue example

```bash
RPUSH queue "task1"
RPUSH queue "task2"
LPOP queue
```

Result:

```javascript
"task1"
```

`"task2"` is left.
This is how a **FIFO queue (first in, first out)** is implemented.

### A stack example

```bash
LPUSH stack "item1"
LPUSH stack "item2"
LPOP stack
```

Result:

```javascript
"item2"
```

This is how a **LIFO stack (last in, first out)** works.

### Additional capabilities

- The `BLPOP` and `BRPOP` commands are **blocking versions**: they wait for an element to appear (handy for asynchronous queues).
- `LPUSHX` and `RPUSHX` add an element **only if the list already exists**.
- `LSET` lets you change an element by index.

### Internal structure

Redis stores lists in two formats:

1. **Quicklist**, the main structure: a combination of a doubly linked list and a ziplist (a compact array).
2. **Ziplist (deprecated)**, used for very short lists.

Quicklist picks the optimal storage method:
if there are few elements, they're stored compactly in memory,
as the list grows, Redis automatically "unpacks" it into a more efficient form.

### Uses

- Task queues between services
- Storing a feed of messages or actions
- Implementing undo/redo
- Temporary log buffers

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