Modify rolo from this chapter so that a person running the program can keep their phone book file in whatever directory they prefer. This can be done by requiring that the user have set a variable called PHONEBOOK to be the name of the phone book file. Check to make sure that it's a valid file and default to the phone book file being in their $HOME directory if the variable's not set.

Question

Here is an example:
$ PHONEBOOK=/users/steve/personal lu Gregory
Gregory 973-747-0370
$ PHONEBOOK=/users/pat/phonebook lu Toritos
El Toritos 973-945-2236
$
In the preceding example, we assume that the user steve has been granted read access to pat's phone book file.
Solution

Answer 1

This is easily done using the same variable assignment shown in example 1 of this chapter, so the key line is
phonebook=${PHONEBOOK:-$HOME/phonebook}
Then a test to see if it exists and is readable can be combined in a single conditional:
if [ ! -r $phonebook ] ; then
echo "Error: $phonebook doesn't exist or isn't readable"
exit 1
f