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/letters.txt <<'SED_INPUT_1'
red
blue
green
SED_INPUT_1

sed 'b done
s/red/RED/
:done
s/blue/BLUE/' data/letters.txt