Open URLs without prefix 'http://' from command line I can open a URL from command as:

open http://www.google.com


If I tried:

open www.google.com
The file ~/www.google.com does not exist.
Perhaps you meant 'http://www.google.com'?


Nevertheless, it works on Windows like:

start www.google.com


It's not convenient to add 'http://' every time.
How to solve the problem?
As @Mark said,


  A URL must begin with a protocol ie the bit before the : so what you have is not a URL.


You'll need to create your own wrapper for the open command. For example, you can use this function to prepend http:

function openweb() { open http://$1 }


Run with openweb google.com or openweb www.google.com.

Place this in a profile file such as ~/.bash_profile to be available in all interactive shells.