How to force cp to overwrite without confirmation

You can do yes | cp -rf xxx yyy, but my gutfeeling says that if you do it as root - your .bashrc or .profile has an alias of cp to cp -i, most modern systems (primarily RH-derivatives) do that to root profiles.

You can check existing aliases by running alias at the command prompt, or which cp to check aliases only for cp.

If you do have an alias defined, running unalias cp will abolish that for the current session, otherwise you can just remove it from your shell profile.

You can temporarily bypass an alias and use the non-aliased version of a command by prefixing it with \, e.g. \cp whatever

This is probably caused by cp being already aliased to something like cp -i. Calling cp directly should work:

/bin/cp -rf /zzz/zzz/* /xxx/xxx

Another way to get around this is to use the yes command:

yes | cp -rf /zzz/zzz/* /xxx/xxx

As some of the other answers have stated, you probably use an alias somewhere which maps cp to cp -i or something similar. You can run a command without any aliases by preceding it with a backslash. In your case, try

\cp -r /zzz/zzz/* /xxx/xxx

The backslash will temporarily disable any aliases you have called cp.