[CentOS] question on tcl.tk

I am playing with tcl/tk on centso 4.2.
I am trying to trap a signal and I get an error
that invalid command name signal.

My line is:

signal trap SIGCONT ReadMessage

where ReadMessage is a proc

Is centos 4.2 missing a package or some thing for tcl?
The example I found did not mention any restrictions.

Any ideas, thank you.

Jerry
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