[Feature Request]: add UNION to Dockerfile syntax

[fshp]

To reduce the number of layers, combining technique used commands through the operator "&&".

But this operator can not be combined arbitrary commands, only the commands in RUN.

I propose to introduce a new unit construction in Dockerfile syntax, which allows to combine several commands in one commit.

For example:

Instead

RUN apt-get update && \
    apt-get dist-upgrade --no-install-recommends -y

You can write

BEGIN
RUN apt-get update
RUN apt-get dist-upgrade --no-install-recommends -y
END

But such a structure in the current syntax in general is impossible:

BEGIN
ADD binary /binary
RUN /binary
END

[AkihiroSuda]

Starting from Docker 1.13, you can use docker build --squash to squash layers

--squash                     Squash newly built layers into a single new layer

Does it satisfy your requirement?

[fshp]

@AkihiroSuda great!
But this flag is very radical.
It can not combine part. Just everything.

But for my needs that's enough. Thank you.

[thaJeztah]

There's a number of similar issues that were opened in the past, but closed
because the Dockerfile syntax was frozen;

#1554, #1799, #16058

Also this one: #12198, and this one may be relevant here as well #7115

[fshp]

@thaJeztah thanks you for links. It was interesting to read. So I close this.

[FranklinYu]

@thaJeztah The Dockerfile syntax was frozen, but you "unfroze" it in 0725045. So is this feature under consideration now?

[muescha]

i would like to have same syntax like in a bash file (so i can copy and paste the content):

RUN BEGIN
  apt-get update
  apt-get dist-upgrade --no-install-recommends -y
END

or

RUN {
  apt-get update
  apt-get dist-upgrade --no-install-recommends -y
}

[thaJeztah]

Those following this issue may be interested in #34423