'dotnet build' specify main method

Question

I am using dotnet to build a .NET Core C# project from the command line. The project has multiple classes with a main method. Thus I get the error:

$ dotnet build
Microsoft (R) Build Engine version 15.1.548.43366
Copyright (C) Microsoft Corporation. All rights reserved.

Test.cs(18,28): error CS0017: Program has more than one entry point defined. Compile with /main to specify the type that contains the entry point.

Build FAILED.

Passing the /main switch results in the error:

$ dotnet build /main:Test
Microsoft (R) Build Engine version 15.1.548.43366
Copyright (C) Microsoft Corporation. All rights reserved.

MSBUILD : error MSB1001: Unknown switch.
Switch: /main:Test

How can I pass the /main switch to the dotnet command?

Answer 1

You can edit your csproj to define which class to use (inside a PropertyGroup):

<StartupObject>foo.Program2</StartupObject> 

or specify this MSBuild property on the command line via:

$ dotnet build foo.csproj -p:StartupObject=foo.Program2 

where

namespace foo {   class Program2{ public static void Main() {} } } 

Answer 2

Just to add why calling dotnet with /main fails with that error, note that it says "Compile with /main"; /main is a parameter for the compiler (csc.exe), not dotnet build. dotnet build will invoke MSBuild.exe which, in turn, will invoke csc.exe, but you'll need to tell dotnet build what the startup class is so it can tell csc.exe. This is what the accepted answer does.

Alternatively, if you were calling csc.exe directly, you could pass /main to it like so...

csc.exe Program.cs Test.cs /main:TestNamespace.Test