without an input source for STDIN. That seems like an error to me. Making '-i' required also would preclude allowing input exclusively from @ARGV. I modeled the UI somewhat on wget/aria2c/(and very recently curl), where you can pass a few inputs in @ARGV, but can pass an input file for larger batches. Of course the simplest answer is to only allow input from @ARGV and use xargs to feed from other input sources, but that results in less ease of use.