Convert a private key .ppk to .pem on Mac OSX

If you’ve used putty to generate your private key, you may need to convert it to a PEM file instead

Firstly install putty via Homebrew

$ brew install putty

Then convert the file

$ puttygen privatekey.ppk -O private-openssh -o privatekey.pem

Install the key by moving the file to ~/.ssh

$ mv privatekey.pem ~/.ssh