Perca o ${fwcmd}
. Seu arquivo está sendo fornecido ao ipfw como argumento.
ipfw [-cfnNqS] [-p preproc [preproc-flags]] pathname
To ease configuration, rules can be put into a file which is processed using ipfw as shown in the last synopsis line. An absolute pathname must be used. The file will be read line by line and applied as arguments to the ipfw utility.
Tente executar ipfw /etc/ipfw.rules