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Each chained element within an instruction should be on its own line.
PropertyValue
SeverityStyle
CategoryStyle
DefaultEnabled
Auto-fixYes (safe)

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Description

Enforces that chained elements within Dockerfile instructions are placed on separate continuation lines using \. This improves readability and produces cleaner diffs. Applies to three instruction types:
  • RUN — splits &&/|| chain boundaries AND splits multiple --mount= flags
  • LABEL — splits multiple key=value pairs
  • HEALTHCHECK CMD — splits &&/|| chain boundaries (shell form only)

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Examples

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Bad

RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*

RUN --mount=type=cache,target=/var/cache/apt --mount=type=bind,source=go.sum,target=go.sum apt-get update

LABEL org.opencontainers.image.title=myapp org.opencontainers.image.version=1.0 org.opencontainers.image.vendor=acme

HEALTHCHECK CMD curl -f http://localhost/ && wget -qO- http://localhost/health || exit 1

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Good

RUN apt-get update \
	&& apt-get install -y curl \
	&& rm -rf /var/lib/apt/lists/*

RUN --mount=type=cache,target=/var/cache/apt \
	--mount=type=bind,source=go.sum,target=go.sum \
	apt-get update

LABEL org.opencontainers.image.title=myapp \
	org.opencontainers.image.version=1.0 \
	org.opencontainers.image.vendor=acme

HEALTHCHECK CMD curl -f http://localhost/ \
	&& wget -qO- http://localhost/health \
	|| exit 1

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Configuration

Default (no config needed): 
# Enabled by default with min-commands = 2
Require 3+ chained commands before splitting: 
[rules.tally.newline-per-chained-call]
min-commands = 3

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Options

OptionTypeDefaultDescription
min-commandsinteger2Minimum chained commands to trigger chain splitting (>= 2). Applies to RUN and HEALTHCHECK CMD.
LABEL pair splitting and mount splitting always trigger when 2+ elements share a line (not affected by min-commands).

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Skipped Cases

The rule skips the following:
  • Exec form (RUN ["cmd"]) — no shell to parse
  • Heredoc RUN (RUN <<EOF) — chain splitting skipped; mount splitting still applies
  • Non-POSIX shell (PowerShell, cmd) — incompatible syntax
  • Inline heredocs (cat <<EOF && cmd) — reformatting would break heredoc boundaries
  • Single command — no chain to split
  • Already formatted — elements already on separate lines
  • Legacy LABEL format (LABEL key value) — handled by buildkit/LegacyKeyValueFormat
  • prefer-run-heredoc coordination — if prefer-run-heredoc is enabled and the command is a heredoc candidate, chain splitting is skipped to avoid conflicting fixes

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Auto-fix

This rule provides a safe auto-fix. Continuation lines use tab indentation consistent with shell conventions (shfmt --bn): 
tally lint --fix Dockerfile
For combined violations (e.g., a RUN with both multiple mounts and chained commands), all edits are applied atomically in a single fix.