[ns] is there any error?

[mahesh@cs.iitm.ernet.in]

Dear sirs,
        i'm a new user of ns and tcl too. i'm hang up with an error.

	if [expr[$link12 up?] == up] then puts "something"

	here i'm checking whether a link is up and if up i wanna do some
	thing. $link12 is an instance of link.

	sir, Is there any error in the above line.
	
	please help me.....

thanx in advance.
                                                   mahesh.