If you need to either Encode or Decode a Base64 value, there are many ways to achieve this, one of them is directly from your commandline itself!
How to Encode a Base64 value in CLI
echo 'This is a test' | base64
This will output a base64 encoded value of
How to Decode a Base64 value in CLI
echo VGhpcyBpcyBhIHRlc3QK | base64 --decode
This will output a decoded value from our base64 value of
This is a test