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## Output
```text
"ENV key=value" should be used instead of legacy "ENV key value" format
```
## 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
(`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.
```dockerfile
FROM alpine
ARG foo bar
```
✅ Good: use an equals sign to separate key and value.
```dockerfile
FROM alpine
ARG foo=bar
```
❌ Bad: multi-line variable declaration with a space separator.
```dockerfile
ENV DEPS \
curl \
git \
make
```
✅ Good: use an equals sign and wrap the value in quotes.
```dockerfile
ENV DEPS="\
curl \
git \
make"
```
|
