Shell Programming and Scripting

I am trying to write a script to send a customized mail message to the users listed on the command line by login name only if they are logged in. If no users are listed on the command line an error message is printed. In the mail message I use the users real name from /etc/passwd. I am trying to write the mail message using a here document.

This is what I have so far, but I am not getting what I should do at the beginning.
PLease help!

Code:

#!/bin/bash

until who | cut -c1-8 | sort -u | grep -w "$1" > /dev/null
do
if
#this is where I need help!
mail $USER << message
Hello `awk -F\: '{print $5}' /etc/passwd` please ignore this mail. My instructor requires that I send this message as part of an assignment for class 92.312. The current time and date is `time` `date`.

This sounds like a homework question.
I'm closing the thread. Please continue here adhering to the homework posting rules.