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Microsoft Sharepoint 2013 : Administering Sharepoint with Windows Powershell - Basic PowerShell Usage (part 3) - Controlling Output

12/17/2014 8:09:36 PM
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PowerShell Objects

Understanding exactly what an object is can be complicated, but a car provides a useful analogy. Like an object, a car has properties. Properties are information about the object, such as the car’s color, make, model, weight, whether it has been flooded or not, and so on. If you’re given the object car, instead of the word “car,” you can use those properties to make decisions. If you have a group of car objects, you can decide to view only the blue ones by checking the car.color property. That’s one aspect of strings that lets you down. When you get a list of site collections from STSADM, you get text. If you want information that isn’t in the text, you have no way to get more information; and if the information you need is hidden somewhere in that string, you have to do complicated text manipulation to get it out. Objects make this type of work much easier.

Continuing with the analogy, like objects, cars also have methods. Methods are actions you can take with your object. For the car example, a method might be start, accelerate, slowdown, rolldownwindows, driveoffcliff, and so on. Objects are treated the same way — different methods are associated with different object types. The car in your garage is an instance of the object car, and it has different properties than other instances of the car object, such as those in your neighbor’s driveway. Methods are one way in which you interact with the objects. The SPSite object has a dispose method, which flushes it out of RAM. It also has a delete method, which is one way to delete an SPSite object.

PowerShell Pipeline

You’ve already seen how using objects makes PowerShell better than STSADM. The pipeline is another PowerShell feature that enables you to take your scripting up another notch. In particular, it enables you to create the aforementioned one-liners by chaining together the output of one cmdlet to the input of another cmdlet. For example, the Get-SPSite command returns all site collections in the farm. The Get-SPWeb command returns a specific web object. If you needed to retrieve all SPWeb objects, you could chain the Get-SPSite command to the Get-SPWeb command using the PowerShell pipeline. To get all the SPWeb objects on your farm (excluding any within the Central Administration web applications), use the following command (see Figure 5):

FIGURE 5

image
Get-SPSite –Limit ALL | Get-SPWeb –Limit ALL

What are being passed between these commands are objects. You will soon see how you can use the methods and properties of these objects to further control what is passed, and how the recipient cmdlet can filter the incoming object to get to the property on which it needs to act.


BLEEDING ON THE SCREEN
When you run the preceding Get-SPSite/Get-SPWeb one-liners, instead of getting a friendly list of all the webs in your farm you might instead get a screen full of red error messages. This is how PowerShell shows its displeasure. Several things can raise PowerShell’s ire, a fact that will become very evident the more you use PowerShell. In this case, it’s probably caused by a lack of permissions to the Config database or one of the content databases. PowerShell accesses SharePoint and its SQL Server databases with the identity of the user PowerShell is running as, so that user must have permission to whatever he or she is trying to access.
There are two ways to do this. First, you can make the user db_owner on all the SharePoint databases or give the user the SYSADMIN role on the SQL Server instances being used. That works, but from a security standpoint it’s not great. A second, better way is to run the Add-SPShellAdmin cmdlet to give the user permission to the databases to which he or she needs access. This must be run as a user with db_owner rights to the database in question. The Add-SPShellAdmin cmdlet must be run for all users against each database they need to run PowerShell against. You can run Get-Help Add-SPShellAdmin to get more information.

Controlling Output

Armed with a basic understanding of the pipeline and its use of objects, this section takes a look at how to control the output of these objects. While the pipeline passes objects around, the input you provide to PowerShell and the output you expect returned at the end is always text. PowerShell handles this with ease. When an object hits the end of a pipeline, it must be captured to a variable, set to void, or formatted for the screen as text. You have already looked at using variables, so you should be familiar with the concept of capturing. Void is a fancy developer term for nothing, or a null value. You don’t need to worry about void. Formatting, however, is something that you will likely want to wrangle control of in order to view the data you want in a form that makes sense to you.

By default, PowerShell formats the output of an object in a table, with columns representing a handful of the most useful properties of the object. In many cases it is fine to let PowerShell format your objects for display in its own default fashion. When an object makes it to the end of the pipeline, the default formatters automatically take effect, unless overridden.

Consider the default formatting for the SPFarm object using the Get-SPFarm command. In Figure 6, you can see that the Config database Name and Status properties are returned from the SPFarm object, which is the default format for output from that object. However, while those are key properties, they are not the only properties associated with the SPFarm object.

FIGURE 6

image

By controlling the output, you can view additional properties and specify how you want the objects formatted. You control the format using the format commands, the most common of which are Format-List and Format-Table (fl and ft are the respective aliases for these commands). There are a few others, but this section looks at only these two common formatting commands.


A WORD ABOUT ALIASES
As you’re getting up to speed with PowerShell you’ll probably “borrow” several PowerShell scripts from various websites. There’s nothing wrong with that, as long as you properly credit your sources. It’s a great way to learn how to use specific PowerShell cmdlets. You’ll see weird symbols such as ? and %. What does it all mean?
To ease the transition from other languages, such as Windows or Linux shell scripting, PowerShell supports the use of aliases. An alias is an alternative way to reference some PowerShell cmdlets.  If you’re ever reading someone else’s PowerShell code and you see commands you don’t recognize, run the PowerShell cmdlet Get-Alias to determine whether the unknown command is an alias for something else. Because aliases can be confusing, it is recommended that you avoid them while learning PowerShell.

Format-List will display object properties in list format. Each object gets one or more rows to display a property and a value. When you see text fly across the screen during some of your outputs, you can assume that you are looking at objects formatted in list style. The example shown in Figure 7 displays the SPFarm object’s returned properties in List view, after using the Format-List command. The Format-List command also accepts an optional Properties parameter, which enables you to provide a comma-separated list of property names to be displayed. Use Get-Member to get a list of the properties for the object you’re formatting.

FIGURE 7

image

Format-Table will display an object’s properties in tabular fashion. Each object gets a single row and one or more columns depending on what properties should be displayed. The default format for most objects is table style, so simply piping the objects to the Format-Table might not get you much further. What will help is the optional –Property parameter, which accepts a comma-separated list of properties to display. You could choose to display all SPFarm properties using the following command:

Get-SPFarm | Format-Table *

If you do that, however, you will get a result that resembles The Matrix — that is, practically unreadable because you attempted to put too many columns in such a small amount of space. The Format-List command is better for showing a large number of properties. For example, instead of displaying all properties, you can display only the DisplayName, Status, and BuildVersion properties. Figure 8 shows an example result using the following command:

FIGURE 8

image
Get-SPFarm | Format-Table –Property DisplayName, Status, BuildVersion

Additionally, the –Property parameter is assumed to be the default value passed to the Format-Table command. The following example shows the preceding command but using the short name of the Format-Table command and passing the desired properties:

Get-SPFarm | Format-Table DisplayName, Status, BuildVersion

Of course, the output of the preceding two commands is identical.

To learn more, use these two help commands:

Get-Help Format 
Get-Help Out

NOTE To clear the screen, use CLS, which is an alias for Clear-Host.
 
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