Main, args

Often developers may need to run a VB.NET program as a command-line utility. And in this situation, the program usually must accept command-line arguments.

By specifying a string array argument to Main, the program will automatically receive arguments. We can then loop over the array and act upon its elements.

Example

To begin, the Main method is specified as a Sub, as it does not return a value. It is contained in a Module—the name of the module is not important.

Module Module1
    Sub Main(args as String())

        ' Step 1: print length of array.
        Console.WriteLine("Args length is: {0}", args.Length)

        ' Step 2: loop over each argument.
        For Each arg in args

            ' Step 3: print argument and use Select Case to match it.
            Console.WriteLine("Arg is: {0}", arg)
            Select Case arg
                Case "test"
                    Console.WriteLine("TEST ARG")
                Case "test2"
                    Console.WriteLine("TEST2 ARG")
                Case Else
                    Console.WriteLine("Unknown")
            End Select

        Next
        
    End Sub
End Module
dotnet run test test2
Args length is: 2
Arg is: test
TEST ARG
Arg is: test2
TEST2 ARG

Nothing array

In my testing, the args array is never Nothing, even when zero arguments are present. However, it may be worth testing it with IsNothing, depending on where the program will run.

Even though VB.NET is a good choice for programs with Windows Forms user interfaces, it can be used for console programs. And for simple tasks, console programs are an ideal choice.