# Tuesday, August 12, 2008
Time For A Change

It’s getting harder to post useful scripting tips for PowerShell these days as there are so many talented hardcore scripting bloggers around. My day to day is job is not system/network/server administrator; I’m a .NET developer, having started the C# habit about eight or nine years ago with the early CLR 1.0 beta. So, from here on in, I’ve decided that a better direction for me to take from now on is that of a PowerShell developer,  as opposed to a scripter. There are very few (if any?) dedicated PowerShell developer blogs around, and so I figured I should try to fill that gap as best I can. I have a not insignificant amount of experience writing providers, cmdlets and other widgety bits, so it’s a good time to share my experiences. Of course, my way is not “the” way, so please reply with your own experiences/advice/mocking/whatever. ;-)

That said, I am not eschewing scripting altogether – I have some stuff in the pipeline (har-har) concerning areas I’m interested in, like eventing and jobs/remoting.

.NET | Cmdlets | Monad | PowerShell | Providers | PSCX | PSEventing | SharePoint | SnapIns
posted on Tuesday, August 12, 2008 10:03:20 AM (Eastern Daylight Time, UTC-04:00)  #    Comments [0] Trackback
# Thursday, June 05, 2008
PSEventing 1.1 For PowerShell 1.0 Final Release

I took a few hours yesterday to "tidy up my room" so to speak, so I built a nice MSI installer, updated the help, CodePlex Wiki and examples and closed all bugs. This is probably the final release now that PowerShell 2.0 CTP2 has introduced support for eventing, so thanks for all the support.

New Features

  • Multiple named queue support and default queue with -QueueName parameter
  • Better COM support, window message pumping etc.
  • NoFlush / Peek parameter support for queue reading
  • Get-EventQueue command added for viewing queues and their message counts.

Cmdlet Name Changes

  • Get-Event -> Read-Event
  • Connect-EventListener -> Connect-Event
  • Disconnect-EventListener -> Disconnect-Event

Additionally, several niggling bugs closed (including the one where read-event -wait would return immediately with no events).

http://www.codeplex.com/pseventing

For an advanced example: Foreground / Background Swappable Downloads In PowerShell.

CodePlex | Monad | PowerShell | PSEventing
posted on Thursday, June 05, 2008 9:20:10 PM (Eastern Daylight Time, UTC-04:00)  #    Comments [0] Trackback
# Friday, December 14, 2007
My PowerPoint slides from PowerShell Virtual User Group #2

In case anyone is interested, here are my slides in PowerPoint PPTX format from the most recent PS Virtual User Group. It covers the new Path handling infrastructure for PscxCmdlets in the upcoming PowerShell Community Extensions 1.2 and some brief information on my PowerShell Eventing snap-in for PowerShell.

psvug2_oisin_grehan.zip (152 KB)

(updated to a zip: it appears DasBlog will not serve pptx files?)

.NET | Monad | PowerShell | PSCX | PSEventing
posted on Friday, December 14, 2007 11:04:07 AM (Eastern Standard Time, UTC-05:00)  #    Comments [2] Trackback
# Wednesday, December 05, 2007
Foreground/Background Swappable Downloads in PowerShell

Here's another interesting use for my PowerShell Eventing Snap-In, where I'm simulating unix-style foreground/background tasks. In this case, the task is a large download using System.Net.WebClient. Just dot-source the script below and start a download using the Start-Download function, passing the url to the large file and the local path where to save your file (be sure to fully qualify the save path). The download will start immediately and show a progress bar with bytes remaining and a percentage, however you can hit Ctrl+C at any time and the download will continue in the background. You can get back to PowerShell tasks, and bring back up the progress bar by invoking Show-Progress at any time. Use Stop-Download to cancel the currently active download. Only one download can be active at a time, but this could easily be extended to support a pool of downloads (using multiple WebClient objects).

downloads.ps1 (1.85 KB)

  1. #requires -pssnapin pseventing  
  2.  
  3. function Stop-Download {  
  4.     $wc.CancelAsync()  
  5. }  
  6.  
  7. function Start-Download {  
  8.     param(  
  9.         [uri]$Url = $(throw "need Url."),  
  10.         [string]$Path = $(throw "Need save path.")  
  11.     )  
  12.  
  13.     # initialise webclient  
  14.     if (-not $global:wc) {  
  15.         $global:wc = New-Object System.Net.WebClient  
  16.         $var = get-variable wc  
  17.         Connect-EventListener -Variable $var `  
  18.             -EventName DownloadProgressChanged, DownloadFileCompleted         
  19.     }  
  20.  
  21.     if ($wc.IsBusy) {  
  22.         Write-Warning "Currently busy: Please cancel current download or wait until it is completed." 
  23.         return 
  24.     }  
  25.       
  26.     $wc.DownloadFileAsync($url, $path, $path) # last is userstate  
  27.     Write-Host "Download started. Ctrl+C to continue in background." 
  28.     Show-Progress  
  29. }  
  30.  
  31. function Show-Progress {  
  32.     if (-not $wc.IsBusy) {  
  33.         # possibly already completed, clear queue  
  34.         get-event | Out-Null 
  35.         "No active download." 
  36.         return 
  37.     }  
  38.       
  39.     Start-KeyHandler -CaptureCtrlC  
  40.       
  41.     trap [exception] {  
  42.         Stop-KeyHandler  
  43.         Write-Warning "error" 
  44.         $_ 
  45.         return 
  46.     }  
  47.       
  48.     $exiting = $false 
  49.       
  50.       
  51.     while (-not $exiting) {       
  52.         $events = @(Get-Event -Wait)          
  53.         $event = $null;  
  54.           
  55.         # skip to last event  
  56.         foreach ($event in $events) {  
  57.             if ($event.Name -eq "CtrlC") {  
  58.                 break;  
  59.             }  
  60.         }         
  61.           
  62.         switch ($event.Name) {  
  63.             "DownloadProgressChanged" {  
  64.                 $r = $event.args.BytesReceived  
  65.                 $t = $event.args.TotalBytesToReceive  
  66.                 $activity = "Downloading $($event.args.userstate)" 
  67.                 $p = [math]::Ceiling(([double]$r / $t) * 100)  
  68.                 Write-Progress -Activity $activity -PercentComplete $p `  
  69.                     -Status ("{0} of {1} byte(s)" -f $r,$t)  
  70.             }  
  71.             "DownloadFileCompleted" {  
  72.                 Write-Progress -Activity DownloadComplete -Completed  
  73.                 "Complete." 
  74.                 $exiting = $true 
  75.             }  
  76.             "CtrlC" {  
  77.                 "Switching to background downloading. Show-Progress to move to foreground." 
  78.                 $exiting = $true 
  79.             }  
  80.         }         
  81.     }  
  82.     Stop-KeyHandler  
  83. } 
.NET | Monad | PowerShell | PSEventing
posted on Wednesday, December 05, 2007 7:47:42 AM (Eastern Standard Time, UTC-05:00)  #    Comments [0] Trackback
# Sunday, December 02, 2007
Using Windows Forms Controls in PowerShell #1: ListBox

Using Windows Forms controls in PowerShell is a tricky thing, because it only supports very simple event listboxhandling. However, some time ago I wrote a Snap-In to allow anyone to work with .NET events, even asynchronous ones. You can download it from my PSEventing CodePlex project; it comes with full help via the normal PowerShell mechanisms of -? and get-help. Examples are also available online on how to use the project for more complex scenarios. Here's simple demonstration of autogenerating a listbox control filled with choices given as arguments to a simple script:

  1. # as simple as 1,2,3 :-)  
  2. $choice = .\get-choice.ps1 "one","two","three" 

And here is the source to the get-choice.ps1 script itself. This requires PSEventing 1.0 or 1.1 Beta.

  1. #requires -pssnapin pseventing  
  2.  
  3. # http://www.codeplex.com/pseventing (1.0 or 1.1)  
  4.  
  5. param([string[]]$choices = $(throw "please supply a string array of choices"))  
  6.  
  7. if ($choices.length -eq 0) {  
  8.     Write-Warning "cannot be a zero length array." 
  9.     return 
  10. }  
  11.  
  12. # initialize form  
  13. $form = new-object windows.forms.form  
  14. $form.Text = "Choose..." 
  15. $form.MinimizeBox = $false 
  16. $form.MaximizeBox = $false 
  17. $form.AutoSize = $true 
  18. $form.AutoSizeMode = "GrowAndShrink" 
  19.  
  20. # initialize listbox  
  21. $listbox = new-object windows.forms.listbox  
  22. $choices | % { [void]$listbox.items.add($_) }  
  23.  
  24. $form.controls.Add($listbox)  
  25.  
  26. # catch a choice in the listbox (remove -verbose for quiet mode)  
  27. Connect-EventListener -VariableName listbox -EventName SelectedIndexChanged -Verbose  
  28.  
  29. # catch someone closing the form (remove -verbose for quiet mode)  
  30. Connect-EventListener -VariableName form -EventName Closed -Verbose  
  31.  
  32. $form.Show()  
  33.  
  34. # wait for an event while performing sendmessage pumping (or ctrl+c to exit)  
  35. $event = Get-Event -Wait  
  36.  
  37. # don't pollute pipeline (remove in production)  
  38. write-host ($event | ft -auto | out-string)  
  39.  
  40. $form.Dispose()  
  41.  
  42. $choice = $listbox.SelectedItem  
  43.  
  44. # clean up; event listeners will be automatically unhooked ;-)  
  45. $form = $null 
  46. $listbox = $null 
  47.  
  48. # return chosen item, or $null if the form was closed  
  49. if ($event.Name -eq "SelectedIndexChanged") {  
  50.     $choice 
  51. } else {  
  52.     $null # cancelled  
  53. } 
Have fun!
.NET | Monad | PowerShell | PSEventing
posted on Sunday, December 02, 2007 4:48:09 PM (Eastern Standard Time, UTC-05:00)  #    Comments [0] Trackback
# Tuesday, July 17, 2007
PSEventing 1.0 Released

PSEventing 1.0 Released

Trap and respond to synchronous & asynchronous .NET events within your powershell scripts with this easy to use suite of cmdlets.

What's new?


  • A PSEvent object's Source property now contains the PSVariable wrapping the original object which generated the event. This resolves scoping issues with 0.5 whereby it wasn't always possible to reach the original sender by variable name (using get-variable).
  • New-Event cmdlet added for inserting user-generated "events" into the queue. This cmdlet allows attaching an abitrary object payload which is available in the PSEvent's Args.Data property.
  • All event handlers are now AUTOMATICALLY unhooked if the original PSVariable goes out of scope! No more phantom events continually generated if you forget to use the explicit "Disconnect-EventListener" and lose your reference. Simply null out a variable or let it disappear into the scopeless void!
  • and finally, some bugfixes, as listed on the release page.

Pick it up from CodePlex, includes source: http://www.codeplex.com/PSEventing/

 

.NET | Monad | PowerShell | PSEventing
posted on Tuesday, July 17, 2007 9:41:47 AM (Eastern Daylight Time, UTC-04:00)  #    Comments [0] Trackback
# Wednesday, May 16, 2007
New wrapper scripts to make using PSEventing easier

I've included some handy wrapper functions to make working with events and scriptblocks a bit easier - download the example script called "event handling wrapper functions" from the Releases page.

  • Add-EventHandler : Automatically run a scriptblock when the provided event occurs on a given variable (when inside Do-Events loop)
    • Add-EventHandler [-Variable] <PSVariable> [-EventName] <String> [-Script] <ScriptBlock>
  • Remove-EventHandler : Remove all bindings for the specific event from the given variable.
    • Remove-EventHandler [-Variable] <PSVariable> [-EventName] <String>
  • Do-Events : Much like VB's DoEvents command, this function puts PowerShell into a waiting state and will call your ScriptBlocks when your configured events occur. Use Ctrl+C to exit.
    • Do-Events [-ExitImmediately] <Boolean>


NOTE: your ScriptBlocks will only be called if you're inside a Do-Events loop.

1# Add-PSSnapin PSEventing
 
2# $fsw = new-object system.io.filesystemwatcher
3# $fsw.Path = "c:\temp"
4# $fsw.EnableRaisingEvents = $true
 
5# Add-EventHandler (get-variable fsw) deleted {
            param([System.Management.Automation.PSVariable]$variable, [EventArgs]$args)
     ... do stuff ... }
 
6# Do-Events $false

an example how to wire up an event using the wrapper scripts

.NET | Monad | PowerShell | PSEventing
posted on Wednesday, May 16, 2007 7:02:10 PM (Eastern Daylight Time, UTC-04:00)  #    Comments [0] Trackback
# Sunday, May 13, 2007
Wondering how to handle .NET events in PowerShell?

Nrgghg,  I feel another PowerShell project coming on ...  enter PowerShell Eventing 0.5 Beta! With the magic of lightweight codegen, aka LCG, a smidgeon of reflection (well, quite a bit) and some inspiration, I managed to cough up this latest project.

While you cannot directly bind scriptblocks as eventhandlers, you can automatically route events in realtime to a background queue and deal with them in your time with a special Get-Event cmdlet. There is a sample walkthrough on the home page of the Wiki, and you can download a Sql backup script which shows progress reporting, all in script!

PS 1# Add-PSSnapin PSEventing                                                                      
PS 2# $wc = new-object system.net.webclient                                                        
PS 3# get-eventbinding -IncludeUnboundEvents | ft -auto                                            
                                                                                                                        
VariableName   EventName               TypeName  Listening                                                              
------------   ---------               --------  ---------                                                              
wc             Disposed                WebClient     False                                                              
wc             DownloadDataCompleted   WebClient     False                                                              
wc             DownloadFileCompleted   WebClient     False                                                              
wc             DownloadProgressChanged WebClient     False                                                              
wc             DownloadStringCompleted WebClient     False                                                              
wc             OpenReadCompleted       WebClient     False                                                              
wc             OpenWriteCompleted      WebClient     False                                                              
wc             UploadDataCompleted     WebClient     False                                                              
wc             UploadFileCompleted     WebClient     False                                                              
wc             UploadProgressChanged   WebClient     False                                                              
wc             UploadStringCompleted   WebClient     False                                                              
wc             UploadValuesCompleted   WebClient     False                                                              
                                                                                                                                                                                                                                        
PS 4# Connect-EventListener wc disposed -verbose                                                   
VERBOSE: Target is a WebClient                                                                                          
VERBOSE: Now listening for 'disposed' events from $wc                                                                   
PS 5# $wc.Dispose()                                                                                
PS 6# get-event | ft -auto                                                                         
                                                                                                                        
Occurred             Source      Name     Args                                                                          
--------             ------      ----     ----                                                                          
5/13/2007 8:04:20 PM variable:wc Disposed System.EventArgs

Have fun!

.NET | Monad | PowerShell | PSEventing
posted on Sunday, May 13, 2007 8:09:16 PM (Eastern Daylight Time, UTC-04:00)  #    Comments [1] Trackback

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