Can't create shell script since El Capitan

Hi

I have two simple Shell Scripts saved in /usr/bin that I use to keep two folders in sync. They are simple rSync commands and, when run with swatch, keep watch over two folders and keep them in sync.

Since updating to El Capitan, not only have my Shell Scripts disappeared, but when I try to re-write them, I get the following error message:

[ Error writing /usr/bin/DesktopSync.sh: Operation not permitted ]

Any ideas?

Thanks

Andrew