Shell add: Test /dev/null and /dev/tty
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	1.Add null.sh to test /dev/null function
	2.Add tty.sh to test /dev/tty function
Shell add:
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	1.usernum.sh:list the number of user
	2.finduser.sh
		function:detect the user is login or not
		usage:finduser.sh user name
		example:finduser.sh june
	3.trace1.sh
		test the trace function
	note:
		The finduser.sh need to be completed