COMMAND

Introduction and Use Case(s)

The COMMAND command in Redis provides detailed information about all available Redis commands. This includes the arity (number of arguments), the command’s flags, and other metadata. It is particularly useful for clients and developers who need to understand the capabilities or constraints of Redis commands programmatically.

Syntax

  1. COMMAND
  2. COMMAND INFO [command-name ...]
  3. COMMAND COUNT
  4. COMMAND GETKEYS [command-and-args ...]
  5. COMMAND GETKEYSANDFLAGS [command-and-args ...]

Parameter Explanations

  • COMMAND: Without any arguments, it returns a list with details of all Redis commands.
  • INFO [command-name …]: Provides detailed information about specific commands.
  • COUNT: Returns the total number of commands in the Redis server.
  • GETKEYS [command-and-args …]: Extracts keys from the given command and arguments.
  • GETKEYSANDFLAGS [command-and-args …]: Extracts keys and their flags from the given command and arguments.

Return Values

  • COMMAND: Returns an array where each element is a nested array containing metadata about a command.
  • INFO [command-name …]: Returns an array of command details for the specified commands.
  • COUNT: Returns an integer representing the number of commands.
  • GETKEYS [command-and-args …]: Returns an array of keys extracted from the command.
  • GETKEYSANDFLAGS [command-and-args …]: Returns an array of arrays, each containing a key and its associated flags.

Code Examples

  1. dragonfly> COMMAND COUNT
  2. (integer) 178
  4. dragonfly> COMMAND INFO SET
  5. 1) 1) "set"
  6.    2) (integer) -3
  7.    3) 1) write
  8.       2) denyoom
  9.    4) (integer) 1
  10.    5) (integer) 1
  11.    6) (integer) 1
  12.    7) (integer) 1
  14. dragonfly> COMMAND GETKEYS SET mykey myvalue
  15. 1) "mykey"
  17. dragonfly> COMMAND GETKEYSANDFLAGS SET mykey myvalue
  18. 1) 1) "mykey"
  19.    2) (empty array)

Best Practices

  • Use COMMAND INFO to dynamically understand the nature of specific commands, especially when building custom Redis clients.
  • Utilize COMMAND GETKEYS to correctly identify which keys a complex command will operate on, aiding in scripting and debugging.

Common Mistakes

  • Incorrect Arity Handling: Failing to account for the arity of commands, which can lead to improper command usage.
  • Overlooking Command Flags: Ignoring command flags like write or denyoom that dictate how commands behave under certain conditions.

FAQs

How can I find out how many commands my Redis instance supports?

You can use the COMMAND COUNT command to get the total number of commands supported by your Redis instance.

Can I dynamically fetch which keys a command will affect?

Yes, you can use the COMMAND GETKEYS or COMMAND GETKEYSANDFLAGS commands to dynamically determine the keys involved in a command.