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Use SHELL to change the default shell.
PropertyValue
SeverityWarning
CategoryBest Practice
DefaultEnabled
Auto-fixYes (--fix)

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Description

Docker provides a SHELL instruction which does not require overwriting /bin/sh in your container. Instead of using ln -sf to redirect /bin/sh, use the SHELL instruction to set the desired shell.

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Examples

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Problematic code

RUN apk add --update-cache bash=4.3.42-r3
RUN ln -sfv /bin/bash /bin/sh

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Correct code

RUN apk add --update-cache bash=4.3.42-r3
SHELL ["/bin/bash", "-c"]

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Auto-fix

Replaces ln -sf targeting /bin/sh with a SHELL instruction. If the ln command is part of a larger RUN, the ln portion is removed and a SHELL instruction is inserted after. 
# Before
RUN ln -sf /bin/bash /bin/sh && apk add curl

# After (with --fix)
RUN apk add curl
SHELL ["/bin/bash", "-c"]

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Reference