Why are there two pairs of quotes for PowerShell arguments?

Question

I was building a Windows Service that needs to periodically execute PowerShell scripts (*.ps1 -Option Value etc) via C#'s Process and I found this answer here about how to do this, but the example there uses two pairs of quotes (first double " then single ') for the Arguments which is quite confusing:

process.StartInfo.Arguments = "\"&'"+strCmdText+"'\"";

Are they both really necessary and if yes then why?

Answer 1

The use of multiple pairs of quotes in the Arguments property when executing a PowerShell script via C#'s Process is not necessary in most cases. It seems like the code snippet you provided might be overly complex or contain unnecessary quotes.

In general, when setting the Arguments property for a PowerShell script in C#, you typically only need to provide the path to the script file itself. For example:

process.StartInfo.Arguments = "path/to/script.ps1";

This assumes that you have set the FileName property of the ProcessStartInfo object to the path of the PowerShell executable (powershell.exe or pwsh.exe depending on your system).

However, there might be certain cases where you need to pass additional arguments or deal with spaces or special characters in the script path. In such situations, you may need to enclose the path in double quotes. For example:

process.StartInfo.Arguments = "\"path/to/script with spaces.ps1\"";

In this case, the double quotes are used to ensure that the entire path is treated as a single argument.

Based on the code snippet you provided (\"&'"+strCmdText+"'\"), it seems like you are trying to pass a command or script text as an argument rather than a script file path. However, the specific usage of double and single quotes in that snippet appears to be unnecessary and could potentially lead to syntax errors.

To provide a more accurate answer, it would be helpful if you could provide the context or specific requirements for executing the PowerShell script so that I can assist you further.

Answer 2

To offer a more PowerShell-focused answer:

the example there uses two pairs of quotes (first double " then single ') for the Arguments (...) Are they both really necessary and if yes then why?

• The quoting requirements depend on whether the -File or the -Command parameter of the PowerShell CLI (powershell.exe for Windows PowerShell, pwsh for PowerShell (Core) 7+) is used.

  • In the absence of either parameter, powershell.exe assumes -Command, pwsh.exe assumes -File.

  • -Command allows you to pass arbitrary PowerShell commands, with the code optionally spread across multiple arguments.

    • Unescaped " characters are stripped during the initial command-line parsing, but ' characters are passed through as-is.
    • Preserving " as part of the PowerShell code to execute require escaping them as \" (sic; even though PowerShell-internally `" must be used).

  • -File expects the path of a script file (*.ps1) to execute, with any additional arguments being passed as literal values to that script.

    • Only " quoting can be used with syntactic function - any ' characters are used verbatim.

• Fundamentally - with both -File and -Command - a script-file path only needs quoting if it contains metacharacters, notably spaces.

• When quoting is needed, the approaches differ depending on -Command vs. -File:

• -File:

  • Use embedded "..." quoting around the file path (and around any pass-through arguments that need quoting) - escaped as ""..."" for the sake of embedding in the C# verbatim string:

    var scriptPath = @"C:\path with spaces\script.ps1";
    process.StartInfo.Arguments = $@"-File ""{scriptPath}""";
    

• -Command:

  • While embedded '...' quoting, as in the question, could be used, doing so isn't fully robust, unless extra action is taken: ' is a legal character in file names, so a path containing ' would break the command (which could be avoided with extra effort; see the edge case below).

  • Using embedded "..." quoting avoids this problem, given that " isn't valid in file names (at least on Windows). For the reasons stated above, this requires \-escaping the " characters (spaces added for readability):

     var scriptPath = @"C:\path with spaces\script.ps1";
     process.StartInfo.Arguments = $@" -Command "" & \""{scriptPath}\"" "" ";
    

  • Note:

    • If the only operation you're performing is calling a script with literal arguments, there is no reason to use -Command - use -File instead.

    • It is a fundamental syntax requirement in PowerShell (which does't apply to -File) that a quoted command must be called via &, the call operator.

    • The code to execute is passed as a single argument, enclosed in "..." to -Command. This isn't strictly necessary in an invocation that doesn't involve a shell, but avoids whitespace normalization that would result from PowerShell "stitching" multiple arguments back together to form the code to execute.

    • There's a - largely hypothetical - edge case (which does not affect the -File parameter): If you had file paths that contain verbatim tokens such as $foo, they would be subject to - unwanted - string interpolation by PowerShell; in that case, embedded '...' quoting must be used instead, but with any embedded ' chars. escaped as '':

      var scriptPath = @"C:\path with spaces\script.ps1";
      process.StartInfo.Arguments = $@" -Command "" & '{scriptPath.Replace("'", "''")}' "" ";