shell 脚本 请问下cat <<MAYDAY 这句怎样才对啊

#!/bin/sh
#menu.sh
#set the date ,user and hostname up
MYDATE=date +%d/%m/%y
THIS_HOST=hostname -s
USER=whoami
#loop while
while :
do
#clean the screen
tput clear
#here document starts here
cat <<MAYDAY
-------------------------------------------------------------------------
User:$USER Host:$THIS_HOST Date:$MYDATE
-------------------------------------------------------------------------
1: List file in current directory
2: Use the vi editor
3: See who is on the system
H: Help screen
Q: Quit
-------------------------------------------------------------------------
MAYDAY

# here is end the document
echo -e -n "\t Your Choice[1,2,3,H,Q]>"
read CHOICE
case $CHOICE in
    1) ls
        ;;
    2) vi
        ;;
    3) whoami
        ;;
    H|h) 
        cat <<MAYDAY
        This is help screen,but nothing can Help you!
        MAYDAY
        ;;
    Q|q) exit 0
        ;;
    *) echo -e "\t\007 Unknow user response"
        ;;
    esac
echo -e -n "\tHit the return key to continue"
read DUMMY

done

http://bbs.chinaunix.net/thread-2317708-1-1.html