You need to buffer the entire input somewhere. You don't get your hash without consuming the entire input. You can't start feeding the input to the shell, unt

You need to buffer the entire input somewhere. You don't get your hash without consuming the entire input. You can't start feeding the input to the shell, until you verify the hash. You don't want to download it twice, it case it comes back different the second time (or in case your network is slow). At the point that you are verifying the hash, the entire file must exist on your system somewhere. Disk, memory, OCR-friendly printout, whatever. Buffering to memory can only work if the input is "small", whatever that means. And pipelines aren't meant to do this, so you'll have to do something a bit odd (ie, confusing to anyone trying to understand your code) to make it work. So, buffer to disk. . Or, use Perl. Perl solves everything.