Progress in femtosecond laser technology has led to the generation of laser pulses whose envelope varies on a time scale comparable to that of the electromagnetic field itself. Such pulses consist of less than two optical cycles [1]. Under these conditions, the phase of the carrier frequency with respect to the envelope (absolute phase) determines the variation of the laser electric field in time. Since all effects in strong-field laser interaction are driven by the electromagnetic field of the laser, the absolute phase is important for many different topics in laser physics. Experimental evidences of the role of the absolute phase have been obtained in strong-field photoionization [2], using pulses with random absolute phase, and in high-order harmonic generation, using phase-stabilized pulses [3]. In this work we report on single-shot measurement of harmonic spectra generated by few-optical-cycle pulses. The single-shot approach and the excellent stability of the driving pulses allow us to attribute the measured differences in the harmonic spectra to the absolute phase of the driving pulses, randomly changing from one pulse to the other. The experimental results have been interpreted in the framework of the strong-field approximation (SFA) model [4].