sudo - protected directory

[Frank Bax]

The first example in 'man sudo' shows how to list files in a protected 
directory:
        sudo ls /usr/local/protected

I am not sure how I would search the contents of files found in such a 
directory, for example:
        $ sudo ls -l /var/spool/mqueue/
        total 8
        -rw-------  1 root  wheel  2031 Apr 17 02:54 dfo3H6qkaT024430
        -rw-------  1 root  wheel   936 Apr 19 18:22 qfo3H6qkaT024430
        $ sudo grep . /var/spool/mqueue/
How do I get some output from this grep command?