set -euo pipefail
export LC_ALL=C
sed_work=$(mktemp -d "${TMPDIR:-/tmp}/sed-example.XXXXXX")
trap 'rm -rf -- "$sed_work"' EXIT
cd "$sed_work"
mkdir -p data
cat > data/block.txt <<'SED_INPUT_1'
before
BEGIN
red
blue
END
after
SED_INPUT_1

sed -n '/^BEGIN$/,/^END$/p' data/block.txt