在编写 Dockerfile 时，我们可能需要将多条指令合并成一行，这样语法简洁，并且可以减少镜像层数。
比如，我们的 Dockerfile 里面有这样的语句：
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FROM python:2.7-stretch
WORKDIR /xdhuxc/
COPY dingtalk_callback.py /xdhuxc/
COPY requirements.txt /xdhuxc/
COPY settings.py /xdhuxc/
RUN pip install -r requirements.txt -i https://mirrors.aliyun.com/pypi/simple
ENTRYPOINT ["python", "-u", "/xdhuxc/dingtalk_callback.py"]
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我们想把多个 COPY 指令合并成一条，可以改写该 Dockerfile 为如下形式：
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FROM python:2.7-stretch
WORKDIR /xdhuxc/
COPY dingtalk_callback.py requirements.txt settings.py /xdhuxc/
RUN pip install -r requirements.txt -i https://mirrors.aliyun.com/pypi/simple
ENTRYPOINT ["python", "-u", "/xdhuxc/dingtalk_callback.py"]
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或者
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FROM python:2.7-stretch
WORKDIR /xdhuxc/
COPY ["dingtalk_callback.py", "requirements.txt", "settings.py", "/xdhuxc/"]
RUN pip install -r requirements.txt -i https://mirrors.aliyun.com/pypi/simple
ENTRYPOINT ["python", "-u", "/xdhuxc/dingtalk_callback.py"]
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路径中包含空格时，必须使用这种形式。
COPY 指令支持通配符，如果复制多个文件时，文件名称本身有规律，则可以使用通配符来实现
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FROM python:2.7-stretch
WORKDIR /xdhuxc/
COPY dingtalk* /xdhuxc/ # 复制所有以 "dingtalk" 开头的文件到 /xdhuxc/ 目录下
RUN pip install -r requirements.txt -i https://mirrors.aliyun.com/pypi/simple
ENTRYPOINT ["python", "-u", "/xdhuxc/dingtalk_callback.py"]
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但要注意，COPY 只能复制目录下的内容，不能复制目录，对于目录的复制，要这样写
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COPY templates/ /scmp/templates
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其中，templates 为目录名
https://codeday.me/bug/20171013/84355.html
https://docs.docker.com/engine/reference/builder/#copy