Datasheet

26 CHAPTER 1
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USING POWERSHELL WITH ACTIVE DIRECTORY
Add Logic to a Script
Logic allows your scripts to do things to the variables you’re using and make deci-
sions about what to do. You need to know two basic logic concepts in order to write
PowerShell scripts: loops and conditionals.
Loops
Loops allow you to go through a collection of items and do something to each
item. For example, if you run the Get-Process cmdlet on one of your servers,
PowerShell displays a list of processes that are currently running on that server.
However, you can assign the output of Get-Process to a variable, using the
following command:
$RunningProcesses = Get-Process
In the $RunningProcesses variable, each process is represented by a di erent
object. You could loop through the objects in this variable and do something to
each object, such as display the process ID of each process. One way to accomplish
this is with the ForEach-Object cmdlet:
$RunningProcesses | ForEach-Object { Write-Host $_.Name : $_.Id }
By piping the $RunningProcesses variable into the ForEach-Object cmdlet, the
ForEach-Object cmdlet can cycle through all the objects.  e command inside
the curly brackets ( {...} ) is executed for each of the objects processed by the loop.
You may recognize the $_ variable from Table 1.5.  e $_ variable references the
current object that the loop is processing. So when $_.Id is used, you’re working
with the Id property on each of the objects in the variable. In this case, we’re calling
the Write-Host cmdlet to output the Name and Id of each process to the screen.
Another type of loop you can use is Do .  e Do loop allows you to loop until
a speci c condition is met.  ere are two types of Do loops: Do ... While and
Do ... Until .
In a Do ... While loop, a block of script code is executed over and over again as long
as something is happening. For example, consider the following script code snippet:
$counter = 0
Do
{
Write-Host “Current Number: $counter”
$counter++;
} While ($counter -lt 3)
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