C#
.NET Core 2.1.401
$ dotnet build -p:LangVersion=7.1
Welcome to .NET Core!
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Learn more about .NET Core: https://aka.ms/dotnet-docs
Use 'dotnet --help' to see available commands or visit: https://aka.ms/dotnet-cli-docs
Telemetry
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The .NET Core tools collect usage data in order to help us improve your experience. The data is anonymous and doesn't include command-line arguments. The data is collected by Microsoft and shared with the community. You can opt-out of telemetry by setting the DOTNET_CLI_TELEMETRY_OPTOUT environment variable to '1' or 'true' using your favorite shell.
Read more about .NET Core CLI Tools telemetry: https://aka.ms/dotnet-cli-telemetry
ASP.NET Core
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Successfully installed the ASP.NET Core HTTPS Development Certificate.
To trust the certificate run 'dotnet dev-certs https --trust' (Windows and macOS only). For establishing trust on other platforms refer to the platform specific documentation.
For more information on configuring HTTPS see https://go.microsoft.com/fwlink/?linkid=848054.
Getting ready...
The template "Console Application" was created successfully.
Processing post-creation actions...
Running 'dotnet restore' on prog/prog.csproj...
Restoring packages for /home/jail/prog/prog.csproj...
Generating MSBuild file /home/jail/prog/obj/prog.csproj.nuget.g.props.
Generating MSBuild file /home/jail/prog/obj/prog.csproj.nuget.g.targets.
Restore completed in 272.51 ms for /home/jail/prog/prog.csproj.
Restore succeeded.
Microsoft (R) Build Engine version 15.8.166+gd4e8d81a88 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.
Restore completed in 63.83 ms for /home/jail/prog/prog.csproj.
prog -> /home/jail/prog/bin/Debug/netcoreapp2.1/prog.dll
Build succeeded.
0 Warning(s)
0 Error(s)
Time Elapsed 00:00:03.71
Program.cs(5,15): error CS8107: Feature 'async main' is not available in C# 7.0. Please use language version 7.1 or greater. [/home/jail/prog/prog.csproj]
CSC : error CS5001: Program does not contain a static 'Main' method suitable for an entry point [/home/jail/prog/prog.csproj]
The build failed. Please fix the build errors and run again.