pfctl_43.sh

echo 'block drop out proto tcp to any port 43' | sudo pfctl -Ef - 

# does two things:

#echo 'block drop out proto tcp to any port 43'

#  - writes a one-line pf firewall rule to stdout
#  - the rule means: drop outbound TCP traffic to any destination on port 43

#  | sudo pfctl -Ef -
  
#  - -f - means “load rules from stdin” because - is stdin
#  - -E means “enable pf” if it is not already enabled
  
#    Remove the temporary rule and restore the normal config:

#  sudo pfctl -f /etc/pf.conf