This is all pretty basic stuff. One thing that always bites me is trying to use sudo to redirect to a protected file. This doesn't work, because the shell is doing the redirection, not sudo:

    sudo cat ~/something.txt | grep 'hello' > ~someoneelse/result.txt

You can get around this by using sudo to run a new shell that does the redirection:

    sudo sh -c "cat ~/something.txt | grep 'hello' > ~someoneelse/result.txt"