Customizing Docker image fails when container environment variables are used

[ioreskovic]

I am trying to customize the image:

    dockerCommands ++= Seq(
      ExecCmd("RUN", "cp", "$JAVA_HOME/lib/security/cacerts", "$HOME/kafka.client.truststore.jks")
    )

Expected behaviour

sbt docker:publishLocal builds an image

Actual behaviour

[info] cp: cannot stat '$JAVA_HOME/lib/security/cacerts': No such file or directory
[info] Removing intermediate container 8b958d8ea255
[error] The command 'cp $JAVA_HOME/lib/security/cacerts $HOME/kafka.client.truststore.jks' returned a non-zero code: 1

Information

• What sbt-native-packager are you using
  1.7.0
• What sbt version
  1.3.8
• What is your build system (e.g. Ubuntu, MacOS, Windows, Debian )
  MaxOS Catalina 10.15.4
• What package are you building (e.g. docker, rpm, ...)
  docker
• What version has your build tool (find out with e.g. rpm --version)
  Docker version 19.03.8, build afacb8b
• What is your target system (e.g. Ubuntu 16.04, CentOS 7):
  Debian

[ppiotrow]

This is not a bug but behaviour of Docker itself. RUN command has two forms, only one is able to interpret variables. See the explanation in this Stackoverflow answer.

Workaround

dockerCommands ++= Seq(
        Cmd("RUN", "echo ${JAVA_HOME}")
),

[info] Step 21/21 : RUN echo ${JAVA_HOME}
[info]  ---> Running in d03391a31013
[info] /docker-java-home/jre

[info] Step 21/21 : RUN ["echo", "${JAVA_HOME}"]
[info]  ---> Running in 9437d5ff2584
[info] ${JAVA_HOME}