这个参数如何在C＃中传递？

Question

I've seen this code snippet but cannot quite figure out why it can successfully run.

class Program
{
    public static void Main()
    {
        var startInfo = new ProcessStartInfo
        {
            FileName = "PowerShell.exe",
            Arguments = @"-NoLogo -NoProfile ""Get-Content Queries.txt"" | Set-Content Output.tsv"
        };

        Console.WriteLine(startInfo.Arguments);

        Process.Start(startInfo);
    }
}

If I try to execute powershell -NoLogo -NoProfile "Get-Content Queries.txt" | Set-Content Output.tsv powershell -NoLogo -NoProfile "Get-Content Queries.txt" | Set-Content Output.tsv directly in the command prompt it would throw error messages but the above code snippet could successfully finish.

How are the double quotes in the code being handled?

Answer 1

When you say command prompt, do you mean cmd.exe? If so, you are dealing with cmd.exe's parsing and it isn't handling the | very well eg:

C:\>dir | foo.txt
'foo.txt' is not recognized as an internal or external command,
operable program or batch file.

If I try your command from a PowerShell V4 prompt, it works fine. Also, the script executed in C# is using PowerShell's command line parsing and not cmd.exe's parsing.

Answer 2

Command line parameters are parsed using spaces as a delimiter which can be of course be a problem for things such as paths which have spaces eg Get-Content Queries.txt . So to get around this, any parameters enclosed in double quotes will avoid this type of parsing-by-space-delimiter.

So why do the double quotes work?

With the code in question, because the string is prefixed with the @ string literal, the double quotes are allowed without escaping. A nice short post on how the @ string literal modifier works (by Jon Skeet no less) can be found at What does an @ before the start of a string literal mean? . To quote a sentence from that:

It basically means, "don't apply any interpretations to characters until the next quote character is reached". So, a verbatim string literal can contain backslashes (without them being doubled-up) and even line separators. To get a double-quote (") within a verbatim literal, you need to just double it...

But copying to the command-line manually doesn't work, what's different?

So when copying this to the command-line, this won't work in exactly the same way because it doesn't include the extra step that Process.Start() takes in wrapping the arguments in (wait for it...) another quote! As described in PowerShell and double quotes on the command line :

Here's some ways to make this work properly:

• Use single quotes:

  powershell.exe C:\\Scripts\\ParamCheck.ps1 -Something 'one two'

• Use a backslash delimiter (even though PowerShell internally uses the left-single-quote `):

  powershell.exe C:\\Scripts\\ParamCheck.ps1 -Something \\"one two\\"

• Use three double quotes:

  powershell.exe C:\\Scripts\\ParamCheck.ps1 -Something """one two"""

References:

• What does an @ before the start of a string literal mean?
• PowerShell and double quotes on the command line
• When Do I Have to Put Double Quotes Around Parameter Values?