Skip to main content

The 30,000 Foot View of the PowerShell Pipeline

By
This is post 2 of 7 in this series.

In simple terms, this is what occurs when you use the PowerShell pipeline. You execute a cmdlet that recovers a specific type of object.  The cmdlet then places one object into the PowerShell pipeline.  This object passes to the next cmdlet in the pipeline.  After that cmdlet is finished with it, it moves to the next cmdlet and so on and so forth.  Once the object has exited the pipeline, the first cmdlet releases the next object into the pipeline.  The important thing to note at this time is that only one object is processed in the pipeline at any one time.

Let’s take a look at a simple example.
PS C:\> Get-SmbShare

Name   ScopeName Path                              Description   
----   --------- ----                              -----------   
ADMIN$ *         C:\WINDOWS                        Remote Admin  
C$     *         C:\                               Default share 
D$     *         D:\                               Default share 
E$     *         E:\                               Default share 
IPC$   *                                           Remote IPC    
print$ *         C:\WINDOWS\system32\spool\drivers Printer Drivers

Six SMB Share objects are presented. Let’s pass these six objects to Where-Object and only keep any share whose Description property is equal to “Default Share”.

PS C:\> Get-SmbShare | Where-Object Description  -eq "Default Share"

Name ScopeName Path Description 
---- --------- ---- ----------- 
C$   *         C:\  Default share
D$   *         D:\  Default share
E$   *         E:\  Default share

As you can see, we only have 3 objects left to work with.  Here is the process for the first few objects.
  1. Get-SMBShare gathered 6 SMB Share objects and placed the first object into the PowerShell Pipeline.  The first object was the SMB Share named Admin$.
  2. The object was passed to the cmdlet Where-Object for processing.
  3. Where object looked at the value of the Description field for this object. The object has a value of “Remote Admin”.
  4. Since this description does not meet our criteria of “Default Share” the object is removed from the pipeline and discarded from memory.
  5. Where-Object signals to Get-SMBShare to send the next object if it has any more.
  6. Get-SMBShare release the next object that has an SMB Share name of C$.
  7. Where-Object receives the object and evaluates the Description property’s value.
  8. Since the value of the Description matches our criteria of “Default Share” The object is put back into the PowerShell pipeline.
  9. Since there are no more cmdlets in the pipeline, the object is sent to the default output device (your monitor). Actually it passes through a complex formatting system, put that is a discussion for another time.
  10. The pipeline signals to the first cmdlet that the pipeline is clear and to send another object if it has one.

T


All of that just by sticking the “|” character between two cmdlets.  The output of the cmdlet on the left becomes the only input for the cmdlet on the right.
Labels:

Comments

Post a Comment

Popular posts from this blog

Sticky Key problem between Windows Server 2012 and LogMeIn

By
This week I instructed my first class using Windows Server 2012 accessed via LogMeIn and discovered a Sticky Key problem every time you press the Shift key. Here is my solution to resolve this.  First off, in the Preferences of LogMeIn for the connection to the Windows Server, click General . Change the Keyboard and mouse priority to Host side user and click Apply at the bottom. On the Windows 2012 server, open the Control Panel – Ease of Access – Change how your keyboard works . Uncheck Turn on Sticky Keys . Click Set up Sticky Keys . Uncheck Turn on Sticky Keys when SHIFT is pressed five times . Click OK twice. If you are using Windows Server 2012 as a Hyper-V host, you will need to redo the Easy of Use settings on each guest operating system in order to avoid the Sticky Key Problem. Updated Information: March 20, 2013 If you continue to have problems, Uncheck Turn on Filter Keys .
6 comments
Read more

With the AD Recycle Bin Turned on, What Happens when you Create a User Account with a Password that does not meet the Password Policy?

By
This was an interesting observation from one of my Windows Server 2012 classes.  While working with the AD Recycle bin in a lab, one of my students discovered some interesting accounts that were created. When he created user accounts that did not meet password complexity requirements, an account is temporarily made and then deleted.  When a new password is provided that meets the password requirements, then a new account is made. We discovered this in two places.  First off in the Active Directory Administrative Center.  This is what caused the initial confusion.  Take a look.  This is in the Deleted Objects OU. You can see multiple deleted accounts for Test2 and one for Test3.  Test3 is a valid, functioning user account.  Using the PowerShell command Get-ADObject –IncludeDeletedObjects –Filter * –Properties ObjectSID we can see that indeed, two accounts were created, with one of them deleted. Notice the RID portion of the SID is different. ...
Post a Comment
Read more

Where did a User’s Account Get Locked Out?

By
Updated: May 15, 2015 When this article was originally published, two extra carriage returns were add causing the code to malfunction.  The code below is correct.   My client for this week’s PowerShell class had a really interesting question. They needed to know where an account is being locked out at. OK, interesting. Apparently users hop around clients and forget to log off, leading to eventual lock out of their accounts. The accounts can be unlocked, but are then relocked after Active Directory replication. This problem is solved in two parts. The first one is to modify the event auditing on the network. The second part is resolved with PowerShell. The first part involves creating a group policy that will encompass your Domain Controllers. In this GPO, make these changes. Expand Computer Configuration \ Policies \ Windows Settings \ Security Settings \ Advanced Audit Policy Configuration \ Audit Policies \ Account Management Double click User Account Management C...
18 comments
Read more