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/spaces.txt <<'SED_INPUT_1'
a  b   c
keep
SED_INPUT_1

sed ':again
s/  / /
t again' data/spaces.txt