Recursively generate all possible combinations from a hash of ranges (e.g. doing a parameter sweep)

recursive_loops.rb

require 'pp'

$ranges = {
  :k => (21..90).step(4).to_a,
  :d => (1..10).to_a
}

def nested_loop(index, opts)
  if index == $ranges.length
    # run command
    pp opts
    return
  end
  key = $ranges.keys[index]
  for value in $ranges[key]
    opts[key] = value
    nested_loop(index + 1, opts)
  end
end

nested_loop(0, {})