LegacyKeyValueFormat
Table of contents
Output
"ENV key=value" should be used instead of legacy "ENV key value" formatDescription
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
(key) and value (value) are separated by an equals sign (=).
Historically, Dockerfiles have also supported a space separator between the key
and the value (for example, ARG key value). This legacy format is deprecated,
and you should only use the format with the equals sign.
Examples
❌ Bad: using a space separator for variable key and value.
FROM alpine
ARG foo bar✅ Good: use an equals sign to separate key and value.
FROM alpine
ARG foo=bar