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A hash is a map of field-value pairs stored under a single key. You can think of each hash as a lightweight object or record: one key holds all the attributes of a user, a product, or any other entity without needing to scatter them across many string keys. Hash commands let you read, write, and introspect individual fields or the entire map in one round-trip.

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HSET

Sets one or more fields on the hash stored at key. If the key does not exist, a new hash is created. Existing fields are overwritten with the new value; brand-new fields are added. Syntax: HSET key field value [field value ...] 
HSET user:1 name Alice age 30 email alice@example.com
# (integer) 3  (three new fields were added)

HSET user:1 age 31
# (integer) 0  (field existed, updated in place)
Returns: Integer — the number of fields that were newly added (not updated).

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HGET

Returns the value of a single field in the hash stored at key. Syntax: HGET key field 
HGET user:1 name
# "Alice"

HGET user:1 phone
# (nil)
Returns: Bulk string — the field value, or nil if the key or field does not exist.

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HDEL

Removes one or more fields from the hash stored at key. Fields that do not exist are silently ignored. Syntax: HDEL key field [field ...] 
HDEL user:1 email
# (integer) 1

HDEL user:1 phone fax
# (integer) 0  (neither field existed)
Returns: Integer — the number of fields that were actually removed.

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HGETALL

Returns all field-value pairs in the hash stored at key as a flat array: field₁, value₁, field₂, value₂, … Syntax: HGETALL key 
HGETALL user:1
# 1) "name"
# 2) "Alice"
# 3) "age"
# 4) "31"
Returns: Array of bulk strings alternating field and value. Returns an empty array if the key does not exist.

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HKEYS

Returns all field names in the hash stored at key. Syntax: HKEYS key 
HKEYS user:1
# 1) "name"
# 2) "age"
Returns: Array of bulk strings — one entry per field. Returns an empty array if the key does not exist.

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HVALS

Returns all values in the hash stored at key, in the same order as HKEYS. Syntax: HVALS key 
HVALS user:1
# 1) "Alice"
# 2) "31"
Returns: Array of bulk strings — one entry per value. Returns an empty array if the key does not exist.

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HLEN

Returns the number of fields in the hash stored at key. Syntax: HLEN key 
HLEN user:1
# (integer) 2
Returns: Integer — the field count, or 0 if the key does not exist.

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HEXISTS

Tests whether a field exists in the hash stored at key. Syntax: HEXISTS key field 
HEXISTS user:1 name
# (integer) 1

HEXISTS user:1 phone
# (integer) 0
Returns: 1 if the field exists, 0 if it does not (or if the key does not exist).

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HMGET

Returns the values of multiple fields in one call. For any field that does not exist, nil is returned in that position. Syntax: HMGET key field [field ...] 
HMGET user:1 name age phone
# 1) "Alice"
# 2) "31"
# 3) (nil)
Returns: Array of bulk strings (or nil entries) in the same order as the requested fields.

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Practical example: user profile

Hashes are a natural fit for storing records. Here’s a complete flow for managing a user profile: 
# Create the profile
HSET user:1 name Alice age 30 email alice@example.com

# Read a single attribute
HGET user:1 name
# "Alice"

# Read the whole record
HGETALL user:1
# 1) "name"
# 2) "Alice"
# 3) "age"
# 4) "30"
# 5) "email"
# 6) "alice@example.com"

# List just the field names
HKEYS user:1
# [name, age, email]

# Check field count
HLEN user:1
# (integer) 3

# Update one field
HSET user:1 age 31

# Remove a field
HDEL user:1 email

# Confirm removal
HEXISTS user:1 email
# (integer) 0
Use HSET with multiple field-value pairs instead of issuing several individual HSET calls. A single round-trip is faster and ensures all fields land atomically.
HGETALL returns fields in insertion order as stored internally. If you need a guaranteed order, use HKEYS to retrieve and sort field names, then fetch values with HMGET.