formatting a string

[Steve Buehler]

I am writing a shell script (#!/bin/sh) that will change some file names 
around but am having trouble formatting a string.  If I have a string like 
this:
20050202
How can I change it to:
2005-02-02

I have about a thousand files so it isn't really feasable for me to be 
changing the names manually.  All of the files are similar to this and I 
have everything in the script to make the change but this one problem.
I have looked into "printf" and "awk/split", but I don't think either one 
of these would work for me.  Maybe one would, but I just couldn't figure it 
out.  Any help would be appreciated.

Thanks
Steve