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Shell Loops and Menus exercise
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- Prepared by Ian Allen - idallen@ncf.ca

Work along with your instructor solving the following problem:

  "You have some friends who need help staying awake while they work
   on their Unix homework.  You volunteer to help keep them awake by
   sending them inter-terminal messages using the Unix "write" command.
   You arrange with each different friend what message they would like
   to see on their screen.  To make your life easier, you write a menu
   program that remembers the message for each of your friends.  You type
   in the name; the script picks the correct message and sends it."

Work with your instructor to build this script:

1) Login twice to ACADAIX, using telnet in two Floppix consoles or
   using two Windows telnet sessions.  (Read the "Using Telnet" web page
   before you use the Windows telnet program to a Unix system!)

   Only ACADAIX has the Unix "banner" command we need for this script.

2) Send yourself a message using "write", e.g. "date | write $USER".
   Make a note of which telnet window receives the output of "write".
   Work in the *other* window while we write this script.
   
   The window receiving the "write" output will be receiving all kinds of
   messages; you won't be able to work in it.  Use the non-write window.

3) Test the "banner" command.  Try this:

       $ banner Hello There!

   You should see the words Hello There! in big letters on your screen.

   Now, pipe the output of banner into write to your other window:

       $ banner Hello There! | write $USER

   You should see the big letters appear in your other telnet window.

4) Pick two or three people in the room to whom you will be sending wake-up
   messages.  Find out their names and Unix userids and what short message
   they would like you to send to their screens.  (The banner command
   output doesn't look good unless you keep your banners to a few words.)

5) Write a looping menu script (similar to the one on p.390 in Chapter 11)
   that prompts you for the name or userid of your friend and then sends
   him/her the appropriate banner message using the "write" command.

   The script might look like this in operation:

       $ ./wakeup

       Enter the name: billy
       You entered: billy
       Writing "Wakie! Wakie!" to "billy" (userid abcd0001).
       Message written to abcd0001.

       Enter the name: bessie
       You entered: bessie
       Writing "Yo! Wazup!" to "bessie" (userid abcd0002).
       Message written to abcd0002.

       Enter the name: becky
       You entered: becky
       Writing "Moo! Moo!" to "becky" (userid abcd0003).
       write: 0803-025 abcd0003 is not logged on.
       Error 255 ocurred writing to abcd0003.

       Enter the name: nosuch
       You entered: nosuch
       ./wakeup: Unrecognized input "nosuch"
       Please enter a recognized name.
       Valid names are: me billy bessie becky

       Enter the name: q
       You entered: q
       Quitting the script - bye now!

6) Test your script with your two or three volunteers.
   Try shell special characters in the input, to make sure you
   have quoted all your variables correctly.