If you want to learn bash scripting in linux read the following book.
Advanced Bash scripting guide[
^]
After that you need to do following steps
1. Monitor the directory for any file addition. You can do it with
"ls" command and its options
2. To rename file use
"mv Original_name_of_file New_name_of_file"
If you don't want to learn scripting and just want the script, search it on google or hire somebody who will do it for you.