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Powershell Objects



PowerShell takes advantage of the underlying .Net framework, using objects instead of text.
Objects in .Net are much the same except for two small differences: the “Parts” are called properties and the “Instructions” are called methods. If we wanted to represent a Windows Service as an object.
Creating PowerShell custom objects is a common task that someone find hard to do. I will show you a sample code to create custom objects.

Creating Custom Objects Using Add-Member
First, let's use Add-Member to create our objects.
$obj=New-Object PSObject
$obj | Add-Member Noteproperty -Name Name -value "Van Don"
$obj | Add-Member Noteproperty -Name Title -value "PowerShell Tutorial"

PowerShell Parameters, Objects, and Formatting


Welcome back! Continuing with your PowerShell Training, the goal of this tutorial is to introduce PowerShell parameters, objects, and formatting output. I’m excited about this tutorial as we begin to define and discover the power of working with objects in PowerShell. By the end of this PowerShell training session you should have a good understanding of what an object is, how we gather information, and how changes are made in the environment.

Launch PowerShell and let’s get started…

Common Parameters (options for cmdlets)

As mentioned before, the standardization of the PowerShell syntax has reduced the learning curve. Cmdlets follow a standard “Verb-Noun” naming convention and also use common parameters. Note: not all cmdlets use these parameters. However, because the PowerShell engine interprets the parameter (not the cmdlet), each common parameter is enacted in the same fashion. Below is a list of the Common Parameters:

  • -whatif – Cmdlet is not actually executed, provides information about “what would happen” if executed.
  • -confirm - Prompt user before executing cmdlet.
  • -Verbose - Provides more detail.
  • -debug - Provides debugging information.
  • -ErrorAction - Instructs cmdlet to perform an action when errors occur. Such as: continue, stop, silently continue, and inquire.
  • -ErrorVariable - Use a specific variable to hold error information. This is in addition to the standard $error variable.
  • -OutVariable - Variable used to hold output information.
  • -OutBuffer - Hold a certain number of objects before calling the next cmdlet in the pipeline.

To view common and other parameters available to the “Set-ExecutionPolicy” cmdlet, type the following at the command prompt:

Set-ExecutionPolicy -<tab>

You can cycle through available parameters, for a cmdlet, by continually pressing the “tab” key. Make sure you are using the dash “-” before pressing tab. Note: not only will you see common parameters but, other parameters that are available as well.

Use the “Get-Help” cmdlet for information on parameters available to a cmdlet. Continuing to use the “Set-ExectutionPolicy” cmdlet, let’s get-help:

Get-Help Set-ExecutionPolicy -Full<enter>

In the “Parameters” section, which provides information on parameters available to the cmdlet, there is a list of the common parameters the cmdlet supports.

Examples:

1. In this example, let’s use the -whatif parameter to see “what would happen” if we used the “Set-ExecutionPolicy” cmdlet:

Set-ExecutionPolicy Unrestricted -whatif<enter>

You are presented with the following: Performing operation “Set-ExecutionPolicy” on Target “Unrestricted”.
This is really cool… before you commit any changes you can verify that the cmdlet is going to do what’s expected. Would have been great if “Format C:” had a -whatif parameter.

2. Using the same cmdlet, choose the -confirm parameter to prompt before executing:

Set-ExecutionPolicy Unrestricted -confirm<enter>

Are you sure you want to perform this action?

  • [Y] Yes (Default is “Y”)
  • [A] Yes to All
  • [N] No
  • [L] No to All
  • [S] Suspend
  • [?] Help

Note: Suspend? This option is very useful. Let’s say you are not sure you want to execute the cmdlet because you are not sure what the “ExecutionPolicy” is set to. You can verify the “ExecutionPolicy” before committing the change:

Set-ExecutionPolicy Unrestricted -confirm<enter>

Are you sure you want…

S<enter> (places the prompt in suspend mode as denoted by “>>”).

>>Get-ExecutionPolicy<enter>
Resricted (or whatever the policy is set to).

>>exit<enter> (Typing “exit” leaves suspend mode and returns to the original command)

Are you sure you want…

Y<enter> (Confirms “Yes” and sets the ExecutionPolicy to “Unrestricted”).

We’ve covered a few examples of what you can do with parameters. Since you know how to “Get-Help” for a cmdlet, it’s easy to discover which parameters are available to any cmdlet. Do some exploring and experimentation before moving on to the “Objects” section.

Introduction to Objects

As discussed in an earlier PowerShell tutorial, PowerShell is object-based not text-based. Since we are working with objects, more information exists than what’s presented (by default) on the command line. That information may not be initially visible; by using PowerShell cmdlets, parameters, and script blocks we can interact with an object to provide us with the information we require.

What is an Object?

An “Object” is something we can gather information from and/or perform an action upon. An object, in PowerShell, consists of properties (information we can gather) and methods (actions we can perform).

I don’t remember where I herd the following explanation but it’s one that sticks with me. As an example, let’s look at a “light bulb.” The object should be obvious, it’s a light bulb. The properties of a light bulb could be color, wattage, and type (florescent, incandescent, or halogen). Methods are the actions we can perform on the object such as; turn on the light bulb and turn off the light bulb. Pretty simple right! Let’s look at an object’s properties and methods.

Ingrain this cmdlet in you head, you will use it constantly: “ Get-Member.” This cmdlet is used to examine what properties and methods are available to an object.

Example 1. Properties and Methods of the “Get-Service” cmdlet.
Type the following to view the properties and methods of the “Get-Service” cmdlet. In this example, the output of “Get-Service” (object) is piped into the “Get-Member” cmdlet.

Get-Service | Get-Member<enter>

PowerShell Training GetMember cmdlet

Get-Member Results

Image 4.1

You should see something similar to Image 4.1. We have identified which properties and methods are available in the “Get-Service” cmdlet. At this point in your PowerShell training if you are not familiar with what’s in the definition column, you are looking at “Data Types.” For example, the “CanStop” property returns a Boolen “Type.” My guess is that the value would either be “True” or “False.” Don’t be concerned with this right now, we will be covering “Types” in another PowerShell tutorial. Just make a mental note that the “Get-Member” cmdlet also returns “data types.”

Example 2. Getting Properties of the “Get-Service” cmdlet.
In this example we refine our search to display only properties by using the -MemberType parameter.

Get-Service | Get-Member -MemberType Property<enter>

Example 3. Getting Methods of the “Get-Service” cmdlet.

Get-Service | Get-Member -MemberType Method<enter>

For a systems administrator, objects are the “Holy Grail” in managing your environment. Why? Because everything in Windows PowerShell is an object. Let me go off the page here for a second to explain. Since we connect to objects and gather information (properties), we are able to compile a report from practically any request our boss throws at us. If the boss requests that a change (method) is made, we are able to make those changes to one or more objects in the environment.

Here’s an example: Overnight, someone has placed a large number of files on the file server that has taken up 50% of the remaining free space. I know, unrealistic right?!? Just follow me on this one. The boss wants a report of all files that were created in the last day. Your answer… “No Problem.”

Get-ChildItem -Path C:\ -Recurse | Where-Object {$_.LastWriteTime -gt “08/25/2007″}<enter>

Let’s dissect what the command is doing:

1. We call the “Get-ChildItem” cmdlet because we want to enumerate the file system.

2. -Path parameter points to the root of C:\ drive as the starting point. The -Recurse parameter means we want all subdirectories and files enumerated.

3. The object returned from the “Get-ChildItem” cmdlet is piped into a script block.

4. Where-Object is a looping statement which finds each object that matches the criteria we are looking for.

What I would like you to notice , what is “LastWriteTime”? Type the following command:

Get-ChildItem | Get-Member<enter>

Do you see a property called “LastWriteTime”? We told the command to find each object with the “LastWriteTime” property that has a value greater than 08/25/2007. “-gt” is an operator that means greater than, we talk more about operators in a later tutorial. I mentioned “Types” before as well, the Definition column states that the “LastWriteTime” property is a “System.DateTime” Type. This means it returns values of this type, which is why we used the “DateTime” type “08/25/2007.” Again, we will discuss “Types” in a later PowerShell tutorial.

Did the method “Turn light bulb On” work? I’m hoping that this discussion on objects is starting to paint the big picture for you. Can you think of what type of properties and methods are associated with user objects in Active Directory? If the boss asks for a report of all disabled users; at this point you should recognize that “user” is an object, more than likely it has a property which returns the status of the account, and a method to either enable or disable it. How about properties and methods associated with computers, printers, and security groups. We are going to get into how we can connect to these objects and enumerate/modify them when we discuss WMI, COM objects, and .NET. But for now, the boss wants us to format the report we gave him in the earlier example.

Formatting output

When we execute a cmdlet we are relying on PowerShell to display results. The “Format-” cmdlets allow us to choose which format to display results in. To get a list of formatting options, type the following command:

Get-Command Format-*<enter>

Format-Custom
Format-List
Format-Table
Format-Wide

Format-Table

“Format-Table” cmdlet displays data in rows and columns, similar to what you would see in an Excel spreadsheet. By default, PowerShell attempts to format the view, but doesn’t always display the best results. For example let’s format the output of the “Get-ChildItem” cmdlet for the “C:\Windows” directory.

Get-ChildItem C:\Windows | Format-Table<enter>

I like the table format, but there seems to be too much white space (spaces) between the columns for my taste. Fortunately, there is a parameter -AutoSize to assist us with white space issues.

Get-ChildItem C:\Windows | Format-Table -AutoSize<enter>

O.k. maybe that wasn’t what you were looking for either. As shown from a previous example, use the <tab> key to cycle through the available parameters for the “Format-table” cmdlet. Expierment with each available parameters to see how format is manipulated.

Format-List

“Format-List” cmdlet displays data in… of course, a list. For example:

Get-ChildItem C:\Windows | Format-List<enter>

By default, we get the following properties: Name, CreationTime, LastWriteTime, and LastAccessTime. The boss looks at the list and requests the full path to the files. Use the -Property parameter to list the “FullName” property. Reminder: use “Get-Member” cmdlet to list the available properties:

Get-ChildItem C:\Windows | Format-List -Property FullName<enter>

If your boss is like mine, I usually hear something like… “that’s great, but now I want the full path to all files and subdirectories, creation date, and last time a file was modified.” Your answer… “No Problem!” To enumerate multiple properties, just separate each property with a comma (,) as shown in this example:

Get-ChildItem C:\Windows -Recurse | Format-List -Property FullName,CreationTime,LastWriteTime<enter>

Note: You can also use the -Property parameter with the “Format-Table” cmdlet to build tables, with each property as a header.

Format-Wide

“Format-Wide” cmdlet compresses results of a list, to fit the screen:

Get-ChildItem C: | Format-Wide<enter>

The results are in list format sorted by column, similar to the old “dir /D” command. You can customize the number of columns using the -Column number parameter:

Get-ChildItem C: | Format-Wide -Column 3<enter>

Group-Object

The “Group-Object” cmdlet allows us to format output information based on groups. For example, there is a property call “Company” for the object returned by the “Get-Process” cmdlet. Let’s assign the “Company” property to a group:

Get-Process | Group-Object Company<enter>

The output groups the information as follows:

· Name – Name provided by the Company property of the Get-Process object.

  • Count – The number of process running from each Company.
  • Group – A truncated list of the processes running.

Here is another example of how to use the “Group-Object” cmdlet. You want to discover which Event IDs are present in the system log:

Get-EventLog System | Group-Object eventid<enter>

Note: The Name column is the Event ID, even though it’s not labeled as such. By default, “Group-Object” places the property you specify in the “Name” column.

Sort-Object

From the example above we are presented with a “Count” column. This indicates the number of occurrences per each Event ID. Just as it sounds, the “Sort-Object” cmdlet provides a mechanism to sort results. In this example, I’m going to further build on the command above to sort from most occurrences to least:

Get-EventLog System | Group-Object eventid | Sort-Object Count -descending<enter>

The results are now sorted from most to least number of occurrences. Couple of things to notice here:

· I sorted on the “Count” column. You could also sort by “Name” or any column you choose.

· As shown above you can pipe results from one cmdlet to another and then another, etc…

Convertto-HTML

I love this cmdlet. It’s not the best html conversion, sometimes the output looks great, sometimes not. It’s just fast and I don’t have to write any code to convert results, like I did in VBScript. Let’s send the results of “Get-Process” to html.

Get-Process | ConvertTo-html<enter>

Well, the cmdlet preformed the conversion but I want the result saved to an html file. I’m going to use the “Out-File” cmdlet to redirect the results into a file. This is similar to using the redirect symbol “>” in the old dos command shell.

Get-Process | ConvertTo-html | out-file “Processes.html”<enter>

To open the .html file use the “Invoke-Item” cmdlet. This is equivalent to clicking on a file where the file type determines which application is launched.

Invoke-Item Processes.html<enter>

The default browser is launched presenting the results saved in the html file. Like I said, doesn’t always look great… But it is fast and the html code can be edited (to look pretty) if desired.

Export-CSV

This is another formatting cmdlet that you are going to love. It takes results and converts it to a csv file. In the following examples we are going to Export the processes and open the file in a spreadsheet. You must have Excel or some other type of spreadsheet installed on the system.

1. Export results to a .csv file”

Get-Process | Export-CSV Processes.csv<enter>

2. Open the spreadsheet:

Invoke-Item Processes.csv<enter>

PowerShell Taining ProcCsv file

Process CSV

Image 4.2

As shown, you can use the “Export-CSV” cmdlet to quickly document and/or create reports. Much more simple that what was required to create the same report in VBScript.

Alright, we got through PowerShell Parameters, Objects, and Formatting. We just hit the tip of the iceberg, we will continue utilizing these cmdlet options as we work in later PowerShell tutorials. Obviously, there are more cmdlet options and parameters we have not covered. PowerShell provides the tools (Get-Help and Get-Member) to explore and learn, so snoop around and get your feet wet.

Hope I was able to shed some light on the advantage objects provide over traditional shell “text string” output. As Objects are the heart of PowerShell and PowerShell scripting, we will be working in depth with objects as we continue our PowerShell training. If you have any comments or questions please use the comment section bellow.