I am trying to get a process handle without success, I have read a lot about that but don't know why I cannot achieve it.
This is what I am doing:
$handle = $Kernel32::OpenProcess(PROCESS_ALL_ACCESS, FALSE, 4548)
I am doing it with admin rights, it seems like it doesn't like the PROCESS_ALL_ACCESS parameter. Any idea?
PowerShell doesn't recognize the symbolic constants you're trying to use there. Use the numeric values instead. For PROCESS_ALL_ACCESS that should be 1056763 or 0x00101ffb (and you also need $false instead of FALSE). However, you probably shouldn't be using PROCESS_ALL_ACCESS in the first place.
Try with PROCESS_QUERY_LIMITED_INFORMATION (numeric value 4096 or 0x1000):
$handle = $Kernel32::OpenProcess(0x1000, $false, 4548)
Related
I have a C# project that I'm consuming with PowerShell.
A method returns an object that have not been fully initialized and that calls P/Invoke under the hood through get properties.
When I call the method, the script crashes because of an accessViolationException that is caused by the call of a property on that partially initialized object, but I didn't call it.
Why do Powershell act like this? is there an option to disable that "eager property evaluation"?
The original issue is the one posted here: https://github.com/ZeBobo5/Vlc.DotNet/issues/330
Add-Type -Path ".\Other\VLC\Vlc.DotNet.Core.dll"
Add-Type -Path ".\Other\VLC\Vlc.DotNet.Core.Interops.dll"
$Cameras = New-Object System.Collections.ArrayList
$Test = New-Object System.Uri("rtsp://192.168.0.50/axis-media/media.amp?camera=1")
$Cameras.Add($Test)
$VlcLibDirPath = (Get-Location).Path + ".\Other\VLC\libvlc_x64"
$VlcLibDir = New-Object System.IO.DirectoryInfo($VlcLibDirPath)
$VlcOpt = "--rtsp-user=admin", "--rtsp-pwd=12345"
$Plyr = New-Object Vlc.DotNet.Core.VlcMediaPlayer($VlcLibDir, $VlcOpt)
for ($i=0; $i -lt $Cameras.Count; $i++)
{
$Plyr.SetMedia($Cameras[$i]) #Fails here with System.AccessViolationException
$Plyr.Play
$Plyr.Stop
}
SetMedia returns a VlcMedia, which contains a Statistics property, which is automatically invoked by PowerShell.
Code for VlcMedia can be found here : https://github.com/ZeBobo5/Vlc.DotNet/blob/develop/src/Vlc.DotNet.Core/VlcMedia/VlcMedia.cs
It's difficult to tell without seeing your code, but there's tons of ways this could be happening. If the object is being displayed at all, the properties are probably all being read.
You should change those to methods, and then they won't get read without specifically being invoked.
Or, change your getters to detect an uninitialized object (you should be doing this already if it's possible for consumers to end up with such an object).
Edit:
With your code posted, it's clear:
$Plyr.SetMedia($Cameras[$i]) #Fails here with System.AccessViolationException
SetMedia returns a VlcMedia, which contains a Statistics property, which is automatically invoked by PowerShell.
Everything returned in PowerShell goes somewhere. If you don't assign it or redirect it, it gets sent to the pipeline.
It seems that you don't want or need the output from this method, so you should either assign it to a variable or dispose of the return in one of a few ways:
[null]$Plyr.SetMedia($Cameras[$i])
$null = $Plyr.SetMedia($Cameras[$i])
$Plyr.SetMedia($Cameras[$i]) | Out-Null
(note: piping to Out-Null is the least performant, which is magnified since you're doing this in a loop)
If you want to use the value later (not shown in your code), assign it and use it later.
I have a strange one I have searched the existing Q&A and haven't found a match.
I have written my functions using parameter validation using the basic format
function FunctioName
{
[CmdletBinding()]
Param(
[parameter(Mandatory)]
[String]$VariableName
)
When I set the parameter to Mandatory as above I get a parameter binding exception indicating a null value was passed. Running the script in debug I can see the function parameter being passed is not null and is a valid string.
When I run the script in the exact same way without the mandatory flag the string is passed into the function and it executes correctly.
Has anyone got any ideas, what could be the issue. This problem is affecting a number of functions in my application interestingly it appears that the affected functions all have only a single parameter functions with multiple parameters do not appear to be affected.
Ok thanks guys for your feedback its much appreciated. BTW i am using powershell 5 .
Further to the issue, looking into it further I found that the variable was being passed to the function as an array of strings, however an empty string value was being appended into the array which I believe was the cause for the issue. This is where it starts to get interesting, I will need to give a bit more background.
The script I am running queries active directory for user attributes meeting specific conditions, those that match I create an array of strings with each value a delimited value of the user,hostname and other attribute properties.
To ensure that I am getting the latest values I use the ASDI GetInfo method,which seems to trigger the odd behavior.
At a high level the functions are
Function GetuserAttr
{
$inscopeusers = New-Object System.Collections.ArrayList
$accountlist = (Get-ADUser -Filter { attribute1 -eq "value"} -Properties attribute1).SamAccountName
foreach ($user in $accountlist)
{
$DN = getDN($user) # basically a funtion I wrote to create ASDI object for user account.
$DN.GetInfo() # this method call appears to cause issues
$attr1 = $DN.Get("Attribute1")
$attr2 = $DN.Get("Attribute2")
$hoststring = "$($user)|$($attr1)|$($attr2)"
$inscopeusers.Add($hoststring) > null
}
return $inscopeusers
}
The string array returned in this function is fed into a number of other functions, one of which is the one that was giving the error that I originally brought up.
The thing is when I use the GetInfo method the array returned by this function contains several null values in the array, when I remove the command the array has no null strings.
Even more strange when I am operating on the array in other functions it appears that the array looses some of its properties when the GetInfo method is used. So for instance I am able to use the foreach loop to iterate through array values but I cannot access an array value by index such as $array[1].
By simply commenting out the GetInfo method call in the function the array returned seems to function normally and you can access array values by index.
I have another function that also uses GetInfo and returns a hash table, when I try to operate on the returned hashtable I cannot access values using a key value such as $hashtable['key'], but I can access them using $hashtable.key. I know this is really weird and can't really think what it could be
Has any one else experienced a similar problem.
You're missing an argument.
Function Test
{
[CmdletBinding()]
Param(
[Parameter(Mandatory=$True)]
[String]
$Variable
)
Write "$Variable"
}
I came across this weird issue in Powershell (not in other languages). Could anyone please explain to me why this happened?
I tried to return a specified number (number 8), but the function keeps throwing everything at me. Is that a bug or by design?
Function GetNum() {
Return 10
}
Function Main() {
$Number10 = GetNum
$number10 #1 WHY NO OUTPUT HERE ??????? I don't want to use write host
$result = 8 # I WANT THIS NUMBER ONLY
PAUSE
return $result
}
do {
$again = Main
Write-Host "RESULT IS "$again # Weird Result, I only want Number 8
} While ($again -eq 10) # As the result is wrong, it loops forever
Is that a bug or by design?
By design. In PowerShell, cmdlets can return a stream of objects, much like using yield return in C# to return an IEnumerable collection.
The return keyword is not required for output values to be returned, it simply exits (or returns from) the current scope.
From Get-Help about_Return (emphasis added):
The Return keyword exits a function, script, or script block. It can be
used to exit a scope at a specific point, to return a value, or to indicate
that the end of the scope has been reached.
Users who are familiar with languages like C or C# might want to use the
Return keyword to make the logic of leaving a scope explicit.
In Windows PowerShell, the results of each statement are returned as
output, even without a statement that contains the Return keyword.
Languages like C or C# return only the value or values that are specified
by the Return keyword.
Mathias is spot on as usual.
I want to address this comment in your code:
$number10 #1 WHY NO OUTPUT HERE ??????? I don't want to use write host
Why don't you want to use Write-Host? Is it because you may have come across this very popular post from PowerShell's creator with the provocative title Write-Host Considered Harmful?
If so, I encourage you to read what I think is a great follow-up/companion piece by tby, titled Is Write-Host Really Harmful?
With this information, it should be clear that as Mathias said, you are returning objects to the pipeline, but you should also be armed with the information needed to choose an alternative, whether it's Write-Verbose, Write-Debug, or even Write-Host.
If I were going to be opinionated about it, I would go with Write-Verbose, altering your function definition slightly in order to support it:
function Main {
[CmdletBinding()]
param()
$Number10 = GetNum
Write-Verbose -Message $number10
$result = 8 # I WANT THIS NUMBER ONLY
PAUSE
$result
}
When you invoke it by just calling $again = Main you'll see nothing on the screen, and $again will have a value of 8. However if you call it this way:
$again = Main -Verbose
then $again will still have the value of 8, but on the screen you'll see:
VERBOSE: 10
likely in differently colored text.
What that gives is not only a way to show the value, but a way for the caller to control whether they see the value or not, without changing the return value of the function.
To drive some of the points in the articles home further, consider that it's not necessarily necessary to invoke your function with -Verbose to get that.
For example, let's say you stored that whole script in a file called FeelingNum.ps1.
If, in addition to the changes I made above, you also add the following to the very top of your file:
[CmdletBinding()]
param()
Then, you still invoked your function "normally" as $again = Main, you could still get the verbose output by invoking your script with -Verbose:
powershell.exe -File FeelingNum.ps1 -Verbose
What happens there is that using the -Verbose parameter sets a variable called $VerbosePreference, and that gets inherited on each function called down the stack (unless it's overridden). You can also set $VerbosePreference manually.
So what you get by using these built-in features is a lot of flexibility, both for you as the author and for anyone who uses your code, which is a good thing even if the only person using it is you.
I have a large list of data (over 1000 different values) and I want the user to be able to select certain values from the list from a PowerShell console.
What is the easiest way from within the console to allow the user to quickly select values?
I would like to do something like tab completion or the ability to use the arrow keys to scroll through the values but I am not sure how to do either of these things.
Any advice would be greatly appreciated.
PowerShell tab completion can be extended to custom parameters and parameter values (in v3). However, this is a property of advanced functions. You can use the ValidateSetAttribute to do that.
Check the Technet help topic on advanced functions: http://technet.microsoft.com/en-us/library/hh847806.aspx
You can replace the tabexpansion (v2) and tabexpansion2 (v3) function in PowerShell to auto complete parameter values outside of advanced functions. You can get a basic definition of this in PowerShell v3 by running
Get-Content function:TabExpansion2
Here is an example of showing custom tab expansion function.
http://www.powershellmagazine.com/2012/11/29/using-custom-argument-completers-in-powershell-3-0/
But, if you want to the user to be able to auto complete values for a Read-Host kind of input, you need to write a proxy for Read-Host to achieve that.
You can, optionally, look at PowerTab module at http://powertab.codeplex.com/
For folks who are looking for a way to do this and are fortunate enough to be using PS v3 (and my apologies for all those required to stay with V2):
The easiest way to achieve this is using the "ValidateSet" option in your input parameters.
function Show-Hello {
param (
[ValidateSet("World", "Galaxy", "Universe")]
[String]$noun
)
$greetingString = "Hello, " + $noun + "!"
Write-Host "`t=>`t" $greetingString "`t<="
}
ValidateSet throws an error if a user attempts to use any other input:
Show-Hello "Solar System"
Show-Hello : Cannot validate argument on parameter 'noun'. The argument `
"Solar System" does not belong to the set "World,Galaxy,Universe" specified `
by the ValidateSet attribute. Supply an argument that is in the set and `
then try the command again.
It also adds tab-completion to your function for that parameter. And if it is the FIRST parameter for your function, you don't even have to type in "-noun" for the tab-complete to make suggestions for its value.
It seems to me that there simply has to be a better way of doing this, but i still haven't found one. And i'm sure i'm not the only one who could use a way to do this: Run an SQL query that only produces one field in one row, then assign that field to a scalar. (In my case, if the query results in more than one field/row, then i have bigger things to worry about than the script breaking).
For example, to get the timestamp from the SQL server, one could use:
my $timestamp;
my $cmd = $dbh->prepare('SELECT cast(now() AS timestamp);') or die $!;
$cmd->execute();
while (my #asd = $cmd->fetchrow_array) { $timestamp = $asd[0] }
Dirty, but it works. But using 4 lines seem a bit much for a simple assignment, especially considering how well perl and postgresql can communicate with eachother via DBI. Sure, i could write a subroutine for it, but isn't there something native that allows me to fetch data as easily as i submit data with $dbh->do() ?
And yes, i did try google.
Usually I write:
$value = $dbh->selectall_arrayref($sql)->[0]->[0];
There's always selectrow_array:
selectrow_array
#row_ary = $dbh->selectrow_array($statement);
#row_ary = $dbh->selectrow_array($statement, \%attr);
#row_ary = $dbh->selectrow_array($statement, \%attr, #bind_values);
This utility method combines prepare, execute and fetchrow_array into a single call.
So something like this:
my $timestamp = $dbh->selectrow_array('select cast(now() as timestamp)');
There's also selectrow_arrayref and selectrow_hashref for similar situations.
From perldoc DBI:
"selectrow_arrayref"
$ary_ref = $dbh->selectrow_arrayref($statement);
$ary_ref = $dbh->selectrow_arrayref($statement, \%attr);
$ary_ref = $dbh->selectrow_arrayref($statement, \%attr, #bind_values);
This utility method combines "prepare", "execute" and
"fetchrow_arrayref" into a single call. It returns the first row of
data from the statement. The $statement parameter can be a previously
prepared statement handle, in which case the "prepare" is skipped.
If any method fails, and "RaiseError" is not set, "selectrow_array"
will return undef.
That will get you most of the way. You still need to do some error checking, but you would be doing that anyway.
Wouldn't fetchrow_array actually only return a scalar as you're only asking for one column?