csproj copy files depending on operating system

Question

For differentiating between Windows & Mac/Linux you can use the $(os) property: this gives you Windows_NT for Windows and UNIX for Mac/Linux.

For differentiating between Mac & Linux, at least on recent versions of MSBuild, you can use RuntimeInformation.IsOSPlatform.

So, combined, your csproj can have something like this:

<ItemGroup>
    <Content Include="libNative.dll" Condition=" '$(OS)' == 'Windows_NT' ">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </Content>
    <Content Include="libNative.so" Condition=" '$([System.Runtime.InteropServices.RuntimeInformation]::IsOSPlatform($([System.Runtime.InteropServices.OSPlatform]::Linux)))' ">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </Content>
    <Content Include="libNative.dylib" Condition=" '$([System.Runtime.InteropServices.RuntimeInformation]::IsOSPlatform($([System.Runtime.InteropServices.OSPlatform]::OSX)))' ">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </Content>
</ItemGroup>

To the best of my knowledge, this should work in all recent versions of .Net Core, Mono and .Net Framework.

In older versions, you’d need to resort to evil trickery for differentiating between Mac & Linux:

For Linux -> Condition=" '$(OS)' == 'Unix' and ! $([System.IO.File]::Exists('/usr/lib/libc.dylib')) "

For Mac -> Condition=" '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib')) "

Sources:

https://github.com/Microsoft/msbuild/issues/539
https://github.com/Microsoft/msbuild/issues/2468

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