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/ids.txt <<'GRP_INPUT_1'
AB-7
AB-42
AB-123
CD-007
xAB-123
GRP_INPUT_1

grep -E '^AB-[0-9]{3}$' data/ids.txt