Let's say you are trying to clone a repository on github.com.

git clone https://JohnDoe:itsasecret@github.com/JohnDoe/example.git

And the following is being returned.

URL using bad/illegal format or missing URL

And 

As the error suggests, the URL being used to clone the repository is invalid.

The easiest way to resolve this is to make note of the URL on github.com.

The example on github.com does not include username and password. Here is how you can include the username.

git clone https://username@github.com/JohnDoe/example.git

And here is how you can include the username and password.

git clone https://username:password@github.com/JohnDoe/example.git