All 7 Lua Scripting questions
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Why would you use a Lua script with Redis instead of just sending several separate commands from your application? What is the difference between EVAL and EVALSHA, and why would you use EVALSHA in a production application? How do you call other Redis commands from within a Lua script, and what restrictions apply to this? How do you manage and organize Lua scripts in a larger application to keep them maintainable as your codebase grows? How would you write a Lua script to implement an atomic rate limiter that checks and increments a request counter in a single operation? What are the performance and blocking implications of running a Lua script in Redis, especially for a script that takes a long time to execute?
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Redis › Lua Scripting

How do you pass keys and other arguments into a Lua script when executing it with the EVAL command?

Beginner

Answer

You specify the actual key names as a group after the script text, preceded by a count of how many keys you are passing, followed by any additional argument values, and within the script itself you access these using the KEYS and ARGV tables, which is the recommended way to reference keys so Redis Cluster can correctly route the script to the right node.
EVAL "return redis.call('set', KEYS[1], ARGV[1])" 1 'mykey' 'myvalue'
Real-world example A rate limiting script receives the specific key to check as KEYS[1] and the maximum allowed requests as ARGV[1], keeping the script generic and reusable across many different rate limited resources.

Common follow-ups: Why should key names always be passed through KEYS rather than hardcoded in the script?;What happens if you provide the wrong number for the key count argument?

Rate Limiting with Redis;Cluster Sharding & Hash Slots
All 7 Lua Scripting questions