  A method is proposed for arbitrarily engineering the high-order harmonic
generation phase achieved by shaping a laser pulse and employing xuv light or x
rays for ionization. This renders the production of bandwidth-limited
attosecond pulses possible while avoiding the use of filters for chirp
compensation. By adding the first 8 Fourier components to a sinusoidal field of
$10^{16}$W/cm$^2$, the bandwidth-limited emission of 8 as is shown to be
possible from a Li$^{2+}$ gas. The scheme is extendable to the zs-scale.
