[CORed]

As others have said, there are plenty of backup solutions available, but if you really want to write your own program, you would be much better off writing it in perl than writing a shell script. You can use the opendir and readdir functions to get file names and the stat function to get at the actual create or modify dates of the files. This will be much more straightforward than trying to parse dates out of ls output using sed or something like that.