how to loop over stdin or file in bash ? (with one single loop)

Question

I have script that can loop over a give file

while IFS=";" read -r a b c
do
  ...
done <"$file"

but I also want user to use stdin.. I know how to read stdin:

while IFS=";" read -r a b c
do
  ...
done <"${1:-/dev/stdin}"

I want to keep loop content unchanged, and to work on the "done" statement to feed it from a file or from stdin.

I am trying to do something like

if [[ "$usefile"=="yes" ]]; then
  data="$file"
else
  data="${1:-/dev/stdin}"
fi

while IFS=";" read -r a b c
do
  ...
done <"$data"

But of course, it does not work at data="${1:-/dev/stdin}" line... the ${} is replaced and fails

tried to use data to store either filename or stdin name.

xout · Answer

I finally found the solution, the done statement have to be changed into

done < "${file:-/dev/stdin}"

if file is provided, it will loop over file content, otherwise it will loop over /dev/stdin

Final script:

# note: leave file empty to loop over stdin.

while IFS=";" read -r a b c
do
  ...
done < "${file:-/dev/stdin}"