How to check if a file is empty in Bash?

Question

I have a file called diff.txt. I Want to check whether it is empty.

I wrote a bash script something like below, but I couldn\'t get it work.

Answer 1

@geedoubleya answer is my favorite.

However, I do prefer this

if [[ -f diff.txt && -s diff.txt ]]
then
  rm -f empty.txt
  touch full.txt
elif [[ -f diff.txt && ! -s diff.txt ]]
then
  rm -f full.txt
  touch empty.txt
else
  echo "File diff.txt does not exist"
fi