# Setup proxy, if required
sudo bash -c 'echo "Acquire::http::Proxy \"http://10.0.0.9:3128\";" > /etc/apt/apt.conf.d/99http-proxy'

# Set environment variables to be used by Curl
export http_proxy=http://10.0.0.9:3128
export https_proxy=http://10.0.0.9:3128

Now install Terraform

curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo apt-key add -

sudo apt-get install software-properties-common

sudo apt-add-repository "deb [arch=$(dpkg --print-architecture)] https://apt.releases.hashicorp.com $(lsb_release -cs) main"

sudo apt update
sudo apt upgrade
sudo apt install terraform