How to output to console from Redis Lua script?

Question

Why doesn't it print hello?

$ redis-cli 127.0.0.1:6379> eval "print( 'hello' )" 0 (nil) 127.0.0.1:6379> 

Launch 2.8.14 on Mac OS X, 2.8.12 on Windows 7.

I am calling in the Lua script from Jedis. To develop them is how to build a ship with a bottle, wear mittens, and someone hit me in the face. My ultimate goal is to somehow recreate a semi-functional development stack using the print trace, debug, whatever commands.

My workaround for my Lua script is a Redis list called "log" returning it to Jedis and then dumping the contents. Kind:

 redis.call( 'del', 'log' ) redis.call( 'rpush', 'log', 'trace statement 1' ) redis.call( 'rpush', 'log', 'trace statement 2' ) ... redis.call( 'lrange', 'log', 0, -1 ) 

Thanks in advance for any advice, help, etc.

Update: I just noticed that "hello" displays through the terminal window for the redis-server executable. Smart. So now I am each terminal for redis server, redis-cli interactive and redis-cli.

Update 2: it turned out that I can print the trace instructions on the redis-cli monitor as follows:

 eval "redis.call( 'echo', 'ugh')" 0 

Which would look like this:

 123.456 [0 127.0.0.1:57709] "eval" "redis.call( 'echo', 'ugh')" "0" 123.456 [0 lua] "echo" "ugh" 

Answer 1

Slap in the palm. Finally it turned out that redis.log (loglevel, message). Which also writes to the output of the redis-server console.

Special thanks to the helpful anonymous voter. You are an excellent person.

Answer 2

There are better ways to develop LUA scripts against redis.

Using lua logs is one way. But you can also publish on-demand logs in the debugging topic by subscribing to it.

You can also set up an IDE with lua intercept points, which I consider to be the best development solution: http://www.trikoder.net/blog/make-lua-debugging-easier-in-redis-87/

Also, remember that automatic testing, unit tests, and / or integrations are useful (running against an instance of debug redis).

Answer 3

using jedis, here is how you can do it .. this is an example of using the set and get commands. you need to include the jar file jedis-2.6.0 in the classpath.

 //jar file - jedis-2.6.0.jar import redis.clients.jedis.Jedis; public class MainClass { public static void main(String[] args){ Jedis jedis = new Jedis("localhost"); System.out.println("Connection to server sucessfully"); jedis.set("name", "a"); System.out.println("Stored string (b4 lua) : "+ jedis.get("name")); String script="redis.call('set','name','b')"; jedis.eval(script); System.out.println("Stored string : "+ jedis.get("name")); } } 

output: Connection to the server successfully Saved string (b4 lua): a Saved string: b