Basic LUA script for selectively moving elements from one Redis list to another.

mov.lua

-- Original use case was a quick and dirty migration of some overbloated repeated jobs
-- from a sidekiq job queue to another/temporary redis list 
-- as part of an incident mitigation.
--
-- usage example:
-- redis.eval("return { KEYS, ARGV }", :keys => ["k1", "k2"], :argv => ["a1", "a2"])
-- EVAL "return ARGV[1]" 2 sidekiq:default moved:default "{\"class\":\"Something\"}"
--
-- KEY[1] is the original list to remove elements from
-- KEY[2] is the other list to move the removed elements to
-- ARGS[1] is the string to match elements against; matched elements are removed while others are ignored


local len = tonumber(redis.call('LLEN', KEYS[1]));

local res = {};
res["total"] = len;

local moved = 0;
local ignored = 0;

while len > 0 do
  -- retrieve the last element in the list
  local entry = redis.call('LINDEX', KEYS[1], -1);

  -- check if entry starts with the given prefix
  if (entry:find(ARGV[1], 1, true) == 1) then
    -- matched
    -- move it from this list to another list
    -- alternatively delete it directly using LREM
    redis.call("LMOVE", KEYS[1], KEYS[2], "RIGHT", "LEFT");

    -- increment count
    moved = moved + 1;
  else
    -- no match
    -- increment ignored count
    ignored = ignored + 1;

    -- move it to the top of this list
    -- our logic is checking the last item in the list
    redis.call("LMOVE", KEYS[1], KEYS[1], "RIGHT", "LEFT");
  end;

  -- decrement loop counter
  len = len - 1;
end;

res["moved"] = moved;
res["ignored"] = ignored;

return res