How can I check if a file is being downloaded?

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http://unix.stackexchange.com – I have a Raspberry Pi which I want to use to automate downloads to a network drive. I would like to restart the machine on a regular basis using cron (I've heard they're not the most stable of things) but obviously, I would prefer not to restart it half way through an incomplete download. I'll probably be downloading using several different methods but one of the ways I'll be using soon is get_iplayer and probably basic wget stuff too. Is there a way I can check if one is in progress? Any advice appreciated. (HowTos)