Catch yum update/upgrade but ignore other update/upgrade in RUN

[cassiussa]

When RUN has the word yum and at some later point the same RUN also contains update all, update, or upgrade, the condition was being met. However this can break some workflows.

For example, the following matches the condition pointlessly because of line 4. No actual yum upgrade happens here but the current conditions make it appear that way.

1 RUN yum install -y python2 py-setuptools \
2    && yum clean all \
3    && easy_install pip \
4    && pip install --upgrade pip

Instead, we can match by spaces and/or tabs using [ \t]+. This way yum, followed by any number of spaces or tabs, followed by update all, update, or upgrade would allow the above Dockerfile to pass but the below Dockerfile would fail correctly or as expected.

1 RUN yum   update \
2    && yum install -y python2 py-setuptools \
3    && yum clean all \
4    && easy_install pip \
5    && pip install --upgrade pip

The same change can probably be made to the other installer methods, such as apt-get etc.

[lphiri]

LGTM!