Ha! I took too long to format my response :). The entr examples from [1] seem to do the same (ls *.rb for example).

[1] http://eradman.com/entrproject/

Also, doesn't entr invoke its command in parallel when there are multiple changes in quick succession? And wouldn't multiple parallel instances of rclone potentially mess up the backup?

(I didn't read any of the man pages)

yep...specifically, use the -d flag in a loop since all it does it exits the process when a new file is added:

  while true; do ls -d src/*.c | entr -d <cmd>; done