• This is a bug report
• This is a feature request
• I searched existing issues before opening this one

Expected behavior

These cases should be allowed:

• --platform=$TARGETPLATFORM
• --platform="$BUILDPLATFORM"
• --platform=${BUILDPLATFORM}
• --platform=${BUILDPLATFORM:-}
• --platform="${BUILDPLATFORM:-}"

Actual behavior

The rule only checks for a literal $BUILDPLATFORM, adding braces, quotes, parameter expansions... or using TARGETPLATFORM results in:

DL3029 warning: Do not use --platform flag with FROM

Steps to reproduce the behavior

Use FROM --platform="${TARGETPLATFORM:-linux/amd64}" and run hadolint.

Dockerfile (if relevant)

FROM --platform="${TARGETPLATFORM:-linux/amd64}" docker.io/library/busybox

Additional environment details (OS, stack version, etc.)

Follow up to #772