buildkit/LegacyKeyValueFormat

ENV key=value should be used instead of the legacy ENV key value format.

Property	Value
Severity	Warning
Category	Style
Default	Enabled
Auto-fix	Yes (`--fix`)

Description

The correct format for declaring environment variables and build arguments in a Dockerfile is ENV key=value and ARG key=value, where the variable name and value are separated by an equals sign. Historically, Dockerfiles have also supported a space separator. This legacy format is deprecated.

Examples

Bad:

ARG foo bar

Good:

ARG foo=bar

Bad:

ENV DEPS \
    curl \
    git \
    make

Good:

ENV DEPS="\
    curl \
    git \
    make"

Auto-fix

The fix replaces the whitespace-separated format with equals format. Quotes are added if the value contains spaces.

# Before
ENV key value
ENV multi word value

# After (with --fix)
ENV key=value
ENV multi="word value"

Reference