@client.event
async def on_member_join(member):
        channel = member.guild.system_channel
        if channel is not None:
            await channel.send('Приветствую, {0.mention}.'.format(member))

@client.command()
async def clear(ctx, amount=None):
    await ctx.channel.purge(limit=int(amount))
    await ctx.channel.send(':: Сообщения успешно удалены')