A simple task (with a simple solution): copy a file to many hosts using say scp. The hosts to copy to are in a text file hosts.txt .

There are many ways to do this, but the following way has the advantage that it is easy to use and that files are copied simultaneously (control the maximum parallelism with the -j switch) which, if you have many hosts, can be a very large saving in time:

xargs -a hosts.txt -d "\n"  parallel -i scp testfile.txt {}:~/  --

Here parallel is GNU Parallel which on Debian/Ubuntu is in the moreutils package.