  Electron beam shaping allows the control of the temporal properties of x-ray
free-electron laser pulses from femtosecond to attosecond timescales. Here we
demonstrate the use of a laser heater to shape electron bunches and enable the
generation of attosecond x-ray pulses. We demonstrate that this method can be
applied in a selective way, shaping a targeted subset of bunches while leaving
the remaining bunches unchanged. This experiment enables the delivery of shaped
x-ray pulses to multiple undulator beamlines, with pulse properties tailored to
specialized scientific applications.
