How to Use Terminal for "Little Snitch" Functionality without Little Snitch

I'm a Terminal newb, and trying to wrap my head around manual "Little Snitch" functionality without using Little Snitch.

From the research I've been doing, I've landed on the fact that I need to utilize pf.conf, however I have no idea how to format my request for Terminal.

I need to block a connection to www.domain.com on port 443. How do I do this?

To permanently block outgoing traffic to specific domains you should create a new anchor file and add it to pf.conf.

1. Create an anchor file org.user.block.out in /private/etc/pf.anchors

   sudo touch /private/etc/pf.anchors/org.user.block.out
   

   with the following content and a trailing empty line

   mybadhosts = "{ www.domain.com, domain.com, www.domain2.com, domain2.com }"
   mybadports = "{ 443, 80 }"
   
   block drop out proto tcp from any to $mybadhosts port $mybadports
   

   The additional domain names in mybadhosts are just an example how to add additional domains. The same goes for port 80 in mybadports.

   A simple but less flexible solution is:

   block drop out proto tcp from any to domain.com port 443
   

2. Modify the file /private/etc/pf.conf but keep a trailing empty line

   original file:

   scrub-anchor "com.apple/*"
   nat-anchor "com.apple/*"
   rdr-anchor "com.apple/*"
   dummynet-anchor "com.apple/*"
   anchor "com.apple/*"
   load anchor "com.apple" from "/etc/pf.anchors/com.apple"
   

   to

   scrub-anchor "com.apple/*"
   nat-anchor "com.apple/*"
   rdr-anchor "com.apple/*"
   dummynet-anchor "com.apple/*"
   anchor "com.apple/*"
   anchor "org.user.block.out"
   load anchor "com.apple" from "/etc/pf.anchors/com.apple"
   load anchor "org.user.block.out" from "/etc/pf.anchors/org.user.block.out"
   

3. Parse and test your anchor file to make sure there are no errors:

   sudo pfctl -vnf /etc/pf.anchors/org.user.block.out
   

4. Now modify /System/Library/LaunchDaemons/com.apple.pfctl.plist from

   <array>
       <string>pfctl</string>
       <string>-f</string>
       <string>/etc/pf.conf</string>
   </array>
   

   to

   <array>
       <string>pfctl</string>
       <string>-e</string>
       <string>-f</string>
       <string>/etc/pf.conf</string>
   </array>
   

   You have to disable System Integrity Protection to accomplish this. After editing the file reenable SIP. After rebooting your Mac pf will be enabled (that's the -e option).

   Alternatively you may create your own launch daemon similar to the answer here: Using Server 5.0.15 to share internet WITHOUT internet sharing.

After a system update or upgrade some of the original files above may have been replaced and you have to reapply all changes.