

          signal action siglist [command]
               Specify the action to take when a Unix signal occurs.
               Siglist is a list of either the symbolic or numeric
               Unix signal (the SIG prefix is optional).  Action is
               one of the following actions to be performed on receipt
               of the signal.

               default - Terminate the process

               ignore - Ignore the signal.

               error - Generate a catchable Tcl error.  It will be as
               if the command that was running returned an error.  The
               error code will be in the form:
                   {UNIX SIG signame}
               For the death of child signal, signame will always be
               SIGCHLD, rather than SIGCLD, to allow writting protable
               code.

               trap - When the signal occures, execute command and
               continue execution if an error is not returned by
               command.  If will be executed in the global context and
               the symbolic signal name (e.g. SIGINT) will be supplied
               in a global variable signalRecieved.  If an error is
               returned, then follow the standard Tcl error mechanism.
               Often command will just do an exit.

               get - Retrieve the current settings of the specified
               signals.  A list will be returned with each element
               containing one of `default', `ignore', `error' or
               `trap' corresponding to each signal in siglist.

               For all signals except SIGCLD, the signal action will
               remain enabled after the specified signal has occured.
               For SIGCLD (also known as SIGCHLD), the signal will not
               be automatically reenable. A wait must be performed
               before issuing another signal command.  Signals are not
               processed until after the completion of the Tcl command
               that is executing when the signal is recieved.
