file IO, is this a bug in Powershell?

Question

I have the following code in Powershell

$filePath = "C:\my\programming\Powershell\output.test.txt"

try
{
    $wStream = new-object IO.FileStream $filePath, [System.IO.FileMode]::Append, [IO.FileAccess]::Write, [IO.FileShare]::Read

    $sWriter = New-Object  System.IO.StreamWriter $wStream

    $sWriter.writeLine("test")
 }

I keep getting error:

Cannot convert argument "1", with value: "[IO.FileMode]::Append", for "FileStream" to type "System.IO.FileMode": "Cannot convert value "[IO.FileMode]::Append" to type "System.IO.FileMode" due to invalid enumeration values. Specify one of the following enumeration values and try again. The possible enumeration values are "CreateNew, Create, Open, OpenOrCreate, Truncate, Append"."

I tried the equivalent in C#,

    FileStream fStream = null;
    StreamWriter stWriter = null;

    try
    {
        fStream = new FileStream(@"C:\my\programming\Powershell\output.txt", FileMode.Append, FileAccess.Write, FileShare.Read);
        stWriter = new StreamWriter(fStream);
        stWriter.WriteLine("hahha");
    }

it works fine!

What's wrong with my powershell script? BTW I am running on powershell

Major  Minor  Build  Revision
-----  -----  -----  --------
3      2      0      2237

The enums are parsed as strings! See https://stackoverflow.com/questions/3289573/passing-enum-values-to-a-function-in-powershell — Micha Wiedenmann, Dec 07 '18 at 13:24

score 23 · Accepted Answer · answered Jan 13 '13 at 06:46

23

Another way would be to use just the name of the value and let PowerShell cast it to the target type:

New-Object IO.FileStream $filePath ,'Append','Write','Read'

answered Jan 13 '13 at 06:46

Shay Levy

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Yup, that's the approach I'd take as well. – Keith Hill Jan 13 '13 at 21:28
2

I can't believe powershell cannot handle an enum in a constructor. They are on version 5.1 now and this still doesn't work! – Brain2000 Dec 02 '18 at 21:21

score 9 · Answer 2 · answered Jan 12 '13 at 16:16

9

When using the New-Object cmdlet and the target type constructor takes in parameters, you should either use the -ArgumentList parameter (of New-Object) or wrap the parameters in parenthesis - I prefer to wrap my constructors with parens:

# setup some convenience variables to keep each line shorter
$path = [System.IO.Path]::Combine($Env:TEMP,"Temp.txt")
$mode = [System.IO.FileMode]::Append
$access = [System.IO.FileAccess]::Write
$sharing = [IO.FileShare]::Read

# create the FileStream and StreamWriter objects
$fs = New-Object IO.FileStream($path, $mode, $access, $sharing)
$sw = New-Object System.IO.StreamWriter($fs)

# write something and remember to call to Dispose to clean up the resources
$sw.WriteLine("Hello, PowerShell!")
$sw.Dispose()
$fs.Dispose()

New-Object cmdlet online help: http://go.microsoft.com/fwlink/?LinkID=113355

answered Jan 12 '13 at 16:16

Goyuix

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You can equally well leave out the parens, because it just expects an object array, optionally preceded by `-ArgumentList`. Your parens just make it a separate expression; is that correct? – mousio Jan 13 '13 at 09:36
7

Parens around an array in PowerShell is effectively a no-op except to act as a token separator. I avoid this syntax `new-object (arg,arg,...)` because it misleads you into believing this is just a C# constructor when it really isn't. It's actually less typing to use `new-object arg,arg,...`. Sorry for being pedantic but I've answered too many questions about why `MyPowerShellFunctionThatTakesThreeParameters(1,2,3)` doesn't work. :-) – Keith Hill Jan 13 '13 at 21:25
1

The powershell decision makers are starting to get on my nerves. One day you're not supposed to use parerenthesis. The next day you are. I see you're using commas for constructors too now. They made this more difficult than it needed to be. – Brain2000 Dec 02 '18 at 21:20

score 5 · Answer 3 · answered Jan 13 '13 at 09:40

5

Yet another way could be to enclose the enums in parens:

$wStream = new-object IO.FileStream $filePath, ([System.IO.FileMode]::Append), `
    ([IO.FileAccess]::Write), ([IO.FileShare]::Read)

answered Jan 13 '13 at 09:40

mousio

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Your way would work if you use parentheses while constructing the FileStream: $wStream = new-object IO.FileStream $filePath([System.IO.FileMode]::Append, [IO.FileAccess]::Write, [IO.FileShare]::Read) – Eyad Aldwaik Apr 12 '19 at 03:45

score 0 · Answer 4 · answered Jan 12 '13 at 16:02

0

If your goal is to write into a logfile or text file, then you could try the supported cmdlets in PowerShell to achieve this?

Get-Help Out-File -Detailed

answered Jan 12 '13 at 16:02

HungryHippos

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file IO, is this a bug in Powershell?

4 Answers4

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