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Detects misspelled or invalid Dockerfile instruction keywords.
PropertyValue
SeverityError
CategoryCorrectness
DefaultEnabled
TypeFail-fast syntax check (exit code 4)

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Description

Dockerfile instructions must be one of the keywords recognized by BuildKit (FROM, RUN, COPY, ADD, WORKDIR, ENV, ARG, EXPOSE, LABEL, CMD, ENTRYPOINT, VOLUME, USER, SHELL, HEALTHCHECK, ONBUILD, STOPSIGNAL, MAINTAINER). A misspelled keyword (e.g., FORM, COPPY, WROKDIR) is silently treated as a comment by the parser, making the resulting image incorrect without any obvious error. This check catches typos early using Levenshtein distance and suggests the closest valid instruction when within edit distance 2. This is a fail-fast check: if any unknown instruction is found, linting aborts with exit code 4.

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Examples

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Bad

FORM alpine:3.20
RUN echo "hello"
Output: 
Error: Dockerfile:1: unknown instruction "FORM" (did you mean "FROM"?)

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Good

FROM alpine:3.20
RUN echo "hello"