1. Install unzip
sudo apt-get install unzip
2. Confirm the latest version number on the terraform website:
https://www.terraform.io/downloads.html
3. Download latest version of the terraform (substituting newer version number if needed)
wget https://releases.hashicorp.com/terraform/0.12.18/terraform_0.12.18_linux_amd64.zip
4. Extract the downloaded file archive
unzip terraform_0.12.18_linux_amd64.zip
5. Move the executable into a directory searched for executables
sudo mv terraform /usr/local/bin/
6. Run it
terraform --version