Batch file string modification

If I had the following code:

set alpha=abcdefghijklmnopqrstuvwxyz

What would I have to 开发者_StackOverflow社区do to %alpha% in order to result in only a, b, c, . . ., z?

If you want to access it via the position you need

set alpha=abcdefghijklmnopqrstuvwxyz
echo %alpha:~0,1%
echo %alpha:~1,1%
echo %alpha:~2,1%
echo %alpha:~25,1%

Explained at set /?