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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def shellinit(cli):
 """Implements the waybill shims in the active shell"""

        output = 'eval echo "Initializing Waybills"'
        if which('docker') is None:
            raise ValueError("Unable to find program 'docker'.  Please make sure it is installed and setup properly")
        for waybill in cli.get_waybills():
            output += ' && source {0}'.format(waybill)
        return output