Powerful lasers are used to drive plasmas in next-generation particle accelerators and X-ray beams. One shortcoming of these beams is that they typically have a range of energy, caused by the gradual rise of laser power from zero to its maximum level. Using plasma foil as an optical switch, this rising time can be reduced effectively, delivering peak laser power to the plasma on a faster time scale. The method of laser-pulse shaping in the interaction of ultra-intense laser pulses with ultra-thin foils is studied by one-dimensional analytical theory and particle-in-cell simulation. Research results indicate that the pulse can be steepened and its width can be shortened effectively due to the self-consistent nonlinear modulation. In comparison to a single foil, a suitable double-foil scheme could optimize the shaping effect, and a transmitted pulse with both shorter duration and larger amplitude is obtained. When the peak amplitude of the incident pulse is higher than the smash threshold of the foil, the rising time of the shaped pulse could be shortened a lot, and the smash of the foil is the direct reason for this shaping effect.