Running PowerShell Scripts From C#

Sometimes the little things can trip up your code, even when you think you are doing all the right things. We recently ran into an issue with a utility that runs an included PowerShell script as part of it operation. When the app was first put into use it seemed to be fine. Recently, it was deployed into a folder with spaces in the name and it began to blow up. Here is a simplified example of what it was running:

void GetAnError()
{
    var ps1File = @"C:\my script folder\script.ps1";
    var startInfo = new ProcessStartInfo()
    {
        FileName = "powershell.exe",
        Arguments = $"-NoProfile -ExecutionPolicy unrestricted \"{ps1File}\"",
        UseShellExecute = false
    };
    Process.Start(startInfo);
}

The error we were getting from PowerShell was along the lines of The term 'C:\my' is not recognized as the name of a cmdlet, function, script file, or operable program, and before looking at the code I figured I had not quoted the file name. But as you can see from the above code, the filename was indeed quoted (I’m not a noob, after all). This puzzled me a bit and it took some digging to see the cause of the error. Here is the fixed code, can you spot the change?

void NoError()
{
    var ps1File = @"C:\my script folder\script.ps1";
    var startInfo = new ProcessStartInfo()
    {
        FileName = "powershell.exe",
        Arguments = $"-NoProfile -ExecutionPolicy unrestricted -file \"{ps1File}\"",
        UseShellExecute = false
    };
    Process.Start(startInfo);
}

When you pass a string to the PowerShell executable it treats it as the Command switch, which is pure PowerShell script. If you want it to explicitly treat it as a script file can use the -File parameter. It just happened to work with paths without spaces, since you can call a script that way. If you do need to pass script text that needs complex quoting (or perhaps line breaks), you can use the EncodedCommand switch, which accepts Base64 encoded content.

void Base64EncodedCommand()
{
    var psCommmand = @"echo ""quoted value"" 
    echo ""Second Line""
    pause";
    var psCommandBytes = System.Text.Encoding.Unicode.GetBytes(psCommmand);
    var psCommandBase64 = Convert.ToBase64String(psCommandBytes);

    var startInfo = new ProcessStartInfo()
    {
        FileName = "powershell.exe",
        Arguments = $"-NoProfile -ExecutionPolicy unrestricted -EncodedCommand {psCommandBase64}",
        UseShellExecute = false
    };
    Process.Start(startInfo);
}

Now you can enjoy launching PowerShell scripts from your C# code without limits.