You can modify /etc/hosts file
That blocks address regardless of the browser.

!/bin/bash

echo "127.0.0.1 www.facebook.com" >> /etc/hosts

or just execute command below
echo "127.0.0.1 www.facebook.com" >> /etc/hosts

Hi,

I have made a script based on the following:

!/bin/sh

sudo nano -e /etc/hosts
127.0.0.1 web.whatsapp.com
127.0.0.1 www.facebook.com
sudo dscacheutil -flushcache
exit 0

However, when i create a policy and upload this .sh file; the page keeps loading. I'm not sure if there is anything wrong in the script. I'm planning to roll out this policy to students' Macbook. Would appreciate if you can help me out.

Thanks.

You could just block the access at the network level and save yourself a lot of hassle (aside from the inevitable complaints from teachers).

Without any sort of network-level content filtering, you should deploy a managed profile for Google Chrome, which along with with blacklisting URLs also would give you enforcement over Safe Browsing, default managed bookmarks, white/blacklist specific Extensions.

https://cloud.google.com/docs/chrome-enterprise/policies/?policy=URLBlacklist