set -euo pipefail
export LC_ALL=C
grep_work=$(mktemp -d "${TMPDIR:-/tmp}/grep-example.XXXXXX")
trap 'rm -rf -- "$grep_work"' EXIT
cd "$grep_work"
mkdir -p data
cat > data/settings.txt <<'GRP_INPUT_1'
# demo

   
PORT=8080
  # note
HOST=local
GRP_INPUT_1

grep -E '^[A-Z_]+=[^=]+$' data/settings.txt