Split string containing command-line parameters into string[] in C#

I have a single string that contains the command-line parameters to be passed to another executable and I need to extract the string[] containing the individual parameters in the same way that C# would if the commands had been specified on the command-line. The string[] will be used when executing another assemblies entry-point via reflection.

Is there a standard function for this? Or is there a preferred method (regex?) for splitting the parameters correctly? It must handle '"' delimited strings that may contain spaces correctly, so I can't just split on ' '.

Example string:

string parameterString = @"/src:""C:\tmp\Some Folder\Sub Folder"" /users:""[email protected]"" tasks:""SomeTask,Some Other Task"" -someParam foo";

Example result:

string[] parameterArray = new string[] { 
  @"/src:C:\tmp\Some Folder\Sub Folder",
  @"/users:[email protected]",
  @"tasks:SomeTask,Some Other Task",
  @"-someParam",
  @"foo"
};

I do not need a command-line parsing library, just a way to get the String[] that should be generated.

Update: I had to change the expected result to match what is actually generated by C# (removed the extra "'s in the split strings)

Solution 1:

It annoys me that there's no function to split a string based on a function that examines each character. If there was, you could write it like this:

    public static IEnumerable<string> SplitCommandLine(string commandLine)
    {
        bool inQuotes = false;

        return commandLine.Split(c =>
                                 {
                                     if (c == '\"')
                                         inQuotes = !inQuotes;

                                     return !inQuotes && c == ' ';
                                 })
                          .Select(arg => arg.Trim().TrimMatchingQuotes('\"'))
                          .Where(arg => !string.IsNullOrEmpty(arg));
    }

Although having written that, why not write the necessary extension methods. Okay, you talked me into it...

Firstly, my own version of Split that takes a function that has to decide whether the specified character should split the string:

    public static IEnumerable<string> Split(this string str, 
                                            Func<char, bool> controller)
    {
        int nextPiece = 0;

        for (int c = 0; c < str.Length; c++)
        {
            if (controller(str[c]))
            {
                yield return str.Substring(nextPiece, c - nextPiece);
                nextPiece = c + 1;
            }
        }

        yield return str.Substring(nextPiece);
    }

It may yield some empty strings depending on the situation, but maybe that information will be useful in other cases, so I don't remove the empty entries in this function.

Secondly (and more mundanely) a little helper that will trim a matching pair of quotes from the start and end of a string. It's more fussy than the standard Trim method - it will only trim one character from each end, and it will not trim from just one end:

    public static string TrimMatchingQuotes(this string input, char quote)
    {
        if ((input.Length >= 2) && 
            (input[0] == quote) && (input[input.Length - 1] == quote))
            return input.Substring(1, input.Length - 2);

        return input;
    }

And I suppose you'll want some tests as well. Well, alright then. But this must be absolutely the last thing! First a helper function that compares the result of the split with the expected array contents:

    public static void Test(string cmdLine, params string[] args)
    {
        string[] split = SplitCommandLine(cmdLine).ToArray();

        Debug.Assert(split.Length == args.Length);

        for (int n = 0; n < split.Length; n++)
            Debug.Assert(split[n] == args[n]);
    }

Then I can write tests like this:

        Test("");
        Test("a", "a");
        Test(" abc ", "abc");
        Test("a b ", "a", "b");
        Test("a b \"c d\"", "a", "b", "c d");

Here's the test for your requirements:

        Test(@"/src:""C:\tmp\Some Folder\Sub Folder"" /users:""[email protected]"" tasks:""SomeTask,Some Other Task"" -someParam",
             @"/src:""C:\tmp\Some Folder\Sub Folder""", @"/users:""[email protected]""", @"tasks:""SomeTask,Some Other Task""", @"-someParam");

Note that the implementation has the extra feature that it will remove quotes around an argument if that makes sense (thanks to the TrimMatchingQuotes function). I believe that's part of the normal command-line interpretation.

Solution 2:

In addition to the good and pure managed solution by Earwicker, it may be worth mentioning, for sake of completeness, that Windows also provides the CommandLineToArgvW function for breaking up a string into an array of strings:

LPWSTR *CommandLineToArgvW(
    LPCWSTR lpCmdLine, int *pNumArgs);

Parses a Unicode command line string and returns an array of pointers to the command line arguments, along with a count of such arguments, in a way that is similar to the standard C run-time argv and argc values.

An example of calling this API from C# and unpacking the resulting string array in managed code can be found at, “Converting Command Line String to Args[] using CommandLineToArgvW() API.” Below is a slightly simpler version of the same code:

[DllImport("shell32.dll", SetLastError = true)]
static extern IntPtr CommandLineToArgvW(
    [MarshalAs(UnmanagedType.LPWStr)] string lpCmdLine, out int pNumArgs);

public static string[] CommandLineToArgs(string commandLine)
{
    int argc;
    var argv = CommandLineToArgvW(commandLine, out argc);        
    if (argv == IntPtr.Zero)
        throw new System.ComponentModel.Win32Exception();
    try
    {
        var args = new string[argc];
        for (var i = 0; i < args.Length; i++)
        {
            var p = Marshal.ReadIntPtr(argv, i * IntPtr.Size);
            args[i] = Marshal.PtrToStringUni(p);
        }

        return args;
    }
    finally
    {
        Marshal.FreeHGlobal(argv);
    }
}

Solution 3:

The Windows command-line parser behaves just as you say, split on space unless there's a unclosed quote before it. I would recommend writing the parser yourself. Something like this maybe:

    static string[] ParseArguments(string commandLine)
    {
        char[] parmChars = commandLine.ToCharArray();
        bool inQuote = false;
        for (int index = 0; index < parmChars.Length; index++)
        {
            if (parmChars[index] == '"')
                inQuote = !inQuote;
            if (!inQuote && parmChars[index] == ' ')
                parmChars[index] = '\n';
        }
        return (new string(parmChars)).Split('\n');
    }