.bat file sorting files into folders
===

For my picture collection I want to have all pictures in a folder automatically sorted into folders by date. Luckily the files are already named after the timestamp:

 - 2012-07-15 12.21.06.jpg
 - 2012-07-15 12.21.26.jpg
 - 2012-07-16 17.12.50.jpg

In this example the two first files should end up in a folder 2012-07-15, the third one in 2012-07-16. I've tried and googled, all I can find is this:

    for %%a in (*.jpg) do (
        md "%%~na" 2>nul
        move "%%a" "%%~na"
    )

But that makes a folder for every file name. I thought of having a variable that has the ten first chars, but get totally confused and frustrated with variable declaration and use in dos. Can anyone help?