gistfile1.rb

# Conditional decrement.
#
# Decrement the value of a key only if the current value is greater than
# a specified value.

require 'rubygems'
require 'redis'

r = Redis.new
cond_decr = <<LUA
    function cond_decr(KEYS,ARGV)
      local value = tonumber(redis('get',KEYS[1]))
      if value == nil then return {err="Value at key is not integer"} end
      if value > tonumber(ARGV[1])
      then
          value = value - 1
          redis('set',KEYS[1],value)
      end
      return value
    end
LUA

r.set(:x,4)
r.eval(cond_decr,0)

5.times {
    puts(r.eval('return cond_decr(KEYS,ARGV)',1,:x,0))
}

--- OUTPUT ---


ruby cond-decr.rb
3
2
1
0
0