Executes command. You should not use an ampersand '&' at the
end of the command. You probably want to use an additional
"exec" at the beginning of command. Without that, the shell
that fvwm invokes to run your command stays until the command
exits. In effect, you'll have twice as many processes running
as you need. Note that some shells are smart enough to avoid
this, but it never hurts to include the "exec" anyway.