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Instruction keywords should use consistent casing throughout the Dockerfile.
PropertyValue
SeverityWarning
CategoryStyle
DefaultEnabled
Auto-fixYes (--fix)

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Description

Instruction keywords should use consistent casing (all lowercase or all uppercase). Using a case that mixes uppercase and lowercase, such as PascalCase or snakeCase, results in poor readability.

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Examples

Bad: 
From alpine
Run echo hello > /greeting.txt
EntRYpOiNT ["cat", "/greeting.txt"]
Good (all uppercase): 
FROM alpine
RUN echo hello > /greeting.txt
ENTRYPOINT ["cat", "/greeting.txt"]
Good (all lowercase): 
from alpine
run echo hello > /greeting.txt
entrypoint ["cat", "/greeting.txt"]

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Auto-fix

The fix changes instruction keywords to match the majority casing in the Dockerfile. 
# Before (majority is uppercase)
FROM alpine
run echo hello

# After (with --fix)
FROM alpine
RUN echo hello

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Reference