stock GetDistanceBetweenVehicles(vehicleid,vehicleid2)
{
    new Float:x1,Float:y1,Float:z1,Float:x2,Float:y2,Float:z2;
    new Float:tmpdis;
    GetVehiclePos(vehicleid,x1,y1,z1);
    GetVehiclePos(vehicleid2,x2,y2,z2);
    tmpdis = floatsqroot(floatpower(floatabs(floatsub(x2,x1)),2)+floatpower(floatabs(floatsub(y2,y1)),2)+floatpower(floatabs(floatsub(z2,z1)),2));
    return floatround(tmpdis);
}

CMD:attach(playerid,params[])
{
	new veh,tra;
	veh=GetPlayerVehicleID(playerid);
	for(new i=0;i<MAX_VEHICLES;i++)
	{
		if(GetDistanceBetweenVehicles(veh,i)>7) return SendClientMessage(playerid, red, "no vehicles.");
  		if(i != veh)
	 		{
		    tra=i;
		    AttachTrailerToVehicle(tra,veh);
		    }
	}
	return 1;
}