dockerfile: heredocs + cmd.exe shell

[fruzitent]

not sure whether is this buildkit frontend issue or just something windows command line cannot deal with

PS>Set-Content ".\Dockerfile" @"
FROM mcr.microsoft.com/windows/nanoserver:ltsc2022
SHELL ["C:\\Windows\\system32\\cmd.exe", "/s", "/c"]
RUN <<EOF
    echo a
    echo b
EOF
"@
PS>docker buildx build . --file ".\Dockerfile" --progress "plain"
#5 [2/2] RUN <<EOF (echo a...)
#5 1.645 a
#5 DONE 2.0s

instead of expected

PS>Set-Content ".\Dockerfile" @"
FROM mcr.microsoft.com/windows/nanoserver:ltsc2022
SHELL ["C:\\Windows\\system32\\cmd.exe", "/s", "/c"]
RUN \
    echo a && \
    echo b
"@
PS>docker buildx build . --file ".\Dockerfile" --progress "plain"
#5 [2/2] RUN     echo a &&     echo b
#5 1.652 a
#5 1.653 b
#5 DONE 2.0s

[profnandaa]

Will take a look and also compare with Linux.
What do you mean by "Powershell is not affected"?

[fruzitent]

servercore (powershell)

FROM mcr.microsoft.com/windows/servercore:ltsc2022
SHELL ["C:\\Windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe", "-Command", "$ErrorActionPreference = 'Stop';", "Set-PSDebug -Trace 1;"]
RUN <<EOF
    Write-Host a
    Write-Host b
EOF

PS>docker buildx build . --file ".\Dockerfile" --no-cache --progress "plain"
#5 [2/2] RUN <<EOF (Write-Host a...)
#5 5.096 DEBUG:    1+ $ErrorActionPreference = 'Stop'; Set-PSDebug -Trace 1;  >>>>
#5 5.096 Write-Host a
#5 5.871 a
#5 5.873 DEBUG:    2+   >>>> Write-Host b
#5 5.874 b
#5 DONE 7.6s

alpine (ash)

FROM docker.io/library/alpine:3.19
SHELL ["/bin/ash", "-ex", "-c"]
RUN <<EOF
    echo a
    echo b
EOF

$ docker buildx build . --file "./Dockerfile" --no-cache --progress "plain"
#5 [2/2] RUN <<EOF (echo a...)
#5 0.497 a
#5 0.497 b
#5 0.497 + echo a
#5 0.497 + echo b
#5 DONE 0.6s

ubuntu (bash)

FROM docker.io/library/ubuntu:24.04
SHELL ["/bin/bash", "-euxo", "pipefail","-c"]
RUN <<EOF
    echo a
    echo b
EOF

$ docker buildx build . --file "./Dockerfile" --no-cache --progress "plain"
#6 [2/2] RUN <<EOF (echo a...)
#6 0.378 + echo a
#6 0.378 + echo b
#6 0.378 a
#6 0.378 b
#6 DONE 0.4s