Skip to main content
Do not refer to an undefined variable.
Superseded by buildkit/UndefinedVar, which provides the same check with typo detection.

​
Description

Ensures that environment variables and build arguments are declared before being used. Undeclared variables can lead to unexpected behavior or build errors.

​
Examples

​
Problematic code

FROM alpine
COPY $foo .

​
Correct code

FROM alpine
ARG foo
COPY $foo .

​
Reference