would look up Pizza in pat's phone book, no matter who is running rolo. The program can find pat's phone book by looking at .rolo in pat's home directory.

Question

Add the -u flag to rolo to allow you to look up someone in another user's phone book (provided that you have read access to it). For example:
$ rolo -u pat Pizza

Answer 1

This is another straightforward task, particularly given that a user's home directory can be specified with the shorthand ~username. Here's the mod:
if [ "$1" = "-u" ] ; then
if [ ! -s "~$2/.rolo" ] ; then
echo "Error: user $2 doesn't have a .rolo file or it's not readable."
exit 1
fi
PHONEBOOK="$(cat ~$2/.rolo)"
shift 2 # get rid of the -u and the username
elif [ -s $HOME/.rolo ] ; then
PHONEBOOK=$(cat $HOME/.rolo)
else
: ${PHONEBOOK:=$HOME/phonebook}
fi