Uniting urls for a download utility (like wget) in one line

If you already have a list of URLs, just add the POST data to that list. Something like:

www.example.com    postdata1
www.foo.com
www.bar.com       second_post_data

Then, instead of using -i, read the file in a bash loop and pass the data to wget:

while read url post; do wget --post-data="$post" $url; done < list.txt

To run them in parallel so that multiple files are downloaded at the same time, use & instead of ;. Careful though, this will launch a separate wget process for each URL.

while read url post; do wget --post-data="$post" $url & done < list.txt

One trick I use for launching this type of thing is keeping track of how many are currently running and only running the next one if the number is below a threshold, 10 for example:

while read url post; do 
 while [[ "$(pgrep -fc wget)" -gt 9 && $c -gt 10 ]]; do sleep 1; done; 
 ((c++));  
 echo "Launching $url ($c)"; 
 wget --post-data="$post" $url >/dev/null 2>&1 && echo "$c finsihed" & 
done < list.txt

That will launch the first 10 URLs, then wait for one to finish and launch the next.

Check out transmission-cli. The usage is as simple as running transmission-cli <torrent-file>, but you can obviously tune it to your needs with several options.

Just a side comment:

Actually you could use many other options, apart from transmission-cli and there will probably appear many other suggestions here (like deluge by Benjamin B. in the comments). I've read somewhere that any well-behaved program should be written so that it can be controlled via command line and the GUI is only an addition to that -- an interface to make the program easier or more convenient to use.