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specs/backgroundinfo/redis_hset_functions.md

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+# 🔑 Redis `HSET` and Related Hash Commands
+
+## 1. `HSET`
+
+* **Purpose**: Set the value of one or more fields in a hash.
+* **Syntax**:
+
+  ```bash
+  HSET key field value [field value ...]
+  ```
+* **Return**:
+
+  * Integer: number of fields that were newly added.
+* **RESP Protocol**:
+
+  ```
+  *4
+  $4
+  HSET
+  $3
+  key
+  $5
+  field
+  $5
+  value
+  ```
+
+  (If multiple field-value pairs: `*6`, `*8`, etc.)
+
+---
+
+## 2. `HSETNX`
+
+* **Purpose**: Set the value of a hash field only if it does **not** exist.
+* **Syntax**:
+
+  ```bash
+  HSETNX key field value
+  ```
+* **Return**:
+
+  * `1` if field was set.
+  * `0` if field already exists.
+* **RESP Protocol**:
+
+  ```
+  *4
+  $6
+  HSETNX
+  $3
+  key
+  $5
+  field
+  $5
+  value
+  ```
+
+---
+
+## 3. `HGET`
+
+* **Purpose**: Get the value of a hash field.
+* **Syntax**:
+
+  ```bash
+  HGET key field
+  ```
+* **Return**:
+
+  * Bulk string (value) or `nil` if field does not exist.
+* **RESP Protocol**:
+
+  ```
+  *3
+  $4
+  HGET
+  $3
+  key
+  $5
+  field
+  ```
+
+---
+
+## 4. `HGETALL`
+
+* **Purpose**: Get all fields and values in a hash.
+* **Syntax**:
+
+  ```bash
+  HGETALL key
+  ```
+* **Return**:
+
+  * Array of `[field1, value1, field2, value2, ...]`.
+* **RESP Protocol**:
+
+  ```
+  *2
+  $7
+  HGETALL
+  $3
+  key
+  ```
+
+---
+
+## 5. `HMSET` (⚠️ Deprecated, use `HSET`)
+
+* **Purpose**: Set multiple field-value pairs.
+* **Syntax**:
+
+  ```bash
+  HMSET key field value [field value ...]
+  ```
+* **Return**:
+
+  * Always `OK`.
+* **RESP Protocol**:
+
+  ```
+  *6
+  $5
+  HMSET
+  $3
+  key
+  $5
+  field
+  $5
+  value
+  $5
+  field2
+  $5
+  value2
+  ```
+
+---
+
+## 6. `HMGET`
+
+* **Purpose**: Get values of multiple fields.
+* **Syntax**:
+
+  ```bash
+  HMGET key field [field ...]
+  ```
+* **Return**:
+
+  * Array of values (bulk strings or nils).
+* **RESP Protocol**:
+
+  ```
+  *4
+  $5
+  HMGET
+  $3
+  key
+  $5
+  field1
+  $5
+  field2
+  ```
+
+---
+
+## 7. `HDEL`
+
+* **Purpose**: Delete one or more fields from a hash.
+* **Syntax**:
+
+  ```bash
+  HDEL key field [field ...]
+  ```
+* **Return**:
+
+  * Integer: number of fields removed.
+* **RESP Protocol**:
+
+  ```
+  *3
+  $4
+  HDEL
+  $3
+  key
+  $5
+  field
+  ```
+
+---
+
+## 8. `HEXISTS`
+
+* **Purpose**: Check if a field exists.
+* **Syntax**:
+
+  ```bash
+  HEXISTS key field
+  ```
+* **Return**:
+
+  * `1` if exists, `0` if not.
+* **RESP Protocol**:
+
+  ```
+  *3
+  $7
+  HEXISTS
+  $3
+  key
+  $5
+  field
+  ```
+
+---
+
+## 9. `HKEYS`
+
+* **Purpose**: Get all field names in a hash.
+* **Syntax**:
+
+  ```bash
+  HKEYS key
+  ```
+* **Return**:
+
+  * Array of field names.
+* **RESP Protocol**:
+
+  ```
+  *2
+  $5
+  HKEYS
+  $3
+  key
+  ```
+
+---
+
+## 10. `HVALS`
+
+* **Purpose**: Get all values in a hash.
+* **Syntax**:
+
+  ```bash
+  HVALS key
+  ```
+* **Return**:
+
+  * Array of values.
+* **RESP Protocol**:
+
+  ```
+  *2
+  $5
+  HVALS
+  $3
+  key
+  ```
+
+---
+
+## 11. `HLEN`
+
+* **Purpose**: Get number of fields in a hash.
+* **Syntax**:
+
+  ```bash
+  HLEN key
+  ```
+* **Return**:
+
+  * Integer: number of fields.
+* **RESP Protocol**:
+
+  ```
+  *2
+  $4
+  HLEN
+  $3
+  key
+  ```
+
+
+
+## 12. `HSCAN`
+
+* **Purpose**: Iterate fields/values of a hash (cursor-based scan).
+* **Syntax**:
+
+  ```bash
+  HSCAN key cursor [MATCH pattern] [COUNT count]
+  ```
+* **Return**:
+
+  * Array: `[new-cursor, [field1, value1, ...]]`
+* **RESP Protocol**:
+
+  ```
+  *3
+  $5
+  HSCAN
+  $3
+  key
+  $1
+  0
+  ```