Unix: confusing use of the Tee -command

Question

Manual states that the tee is a \"pipe fitting\"-tool. The cases [1] confuse me:

1. case

echo \"foo bar\" | sudo tee -a /path/to/some/fi         


        

Answer 1

tee copies stdin to stdout (like cat) and additionally writes everything to the named file. Using it this way with sudo allows one to push information into a privileged mode and - at the same time - monitor whether the right stuff went there.

Also note, that due to the way redirection is handled in the shell the almost equivalent

sudo echo "foo bar" > /path/to/some/file

won't work, since the redirection would be done by the calling user and not by the sudo target user.