Use SHELL to change the default shell DOK-DL4005
Anti-pattern
Major
Docker provides a SHELL instruction allowing for changing the default shell for all subsequent RUN commands.
Manually changing shell is inefficient for two reasons.
First, there is an un-necessary root shell processor invocation.
Second, each RUN instruction in the shell form requires an extra shell command(/bin/sh -c) prefix.
Bad Practice
# Install bash
RUN apk add --update-cache bash=4.3.42-r3
# Use bash as the default shell
RUN ln -sfv /bin/bash /bin/sh
Recommended
# Install bash
RUN apk add --update-cache bash=4.3.42-r3
# Use bash as the default shell
SHELL ["/bin/bash", "-c"]