Depending on where you are using them, parenthesis can be used for several different functions.
In Math
If you remember back in algebra class, we used parenthesis to change the order of processing a math equation. Normally multiplication and division is performed before addition and subtraction
PS C:\> 5+6*10
65
Add some parenthesis, and you change the order of processing.
PS C:\> (5+6)*10
110
In Cmdlets
We can use parenthesis in cmdlets to force other cmdlets to run first. In this example, we have a text file called Names.txt. It contains the names of three computers. Using the cmdlet Get-Content we can see these names.
PS C:\psworks> Get-Content names.txt
TechTour-CL1
TechTour-DC1
Tech-ex1
Now we are going to ask for the BIOS information from each of these clients. there are two ways to do this. The long way is where we specify each computer name one at a time.
PS C:\psworks> Get-WmiObject Win32_Bios -ComputerName Tech-EX1
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 7563-3642-6655-4653-5455-8957-02
Version : VRTUAL - 5001223
Here we would have to type this command 3 times, changing the value of ComputerName name each time. The still long, but not as long method is to provide all the names in a comma separated list.
PS C:\psworks> Get-WmiObject Win32_Bios -ComputerName Tech-EX1, TechTour-DC1, TechTour-CL1
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 7563-3642-6655-4653-5455-8957-02
Version : VRTUAL - 5001223
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 2500-5916-2465-4853-2519-9911-18
Version : VRTUAL - 5001223
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 0214-6255-9078-8822-9031-3935-43
Version : VRTUAL - 5001223
This works, but is very static. We would have to do a lot of typing if we wanted to add more clients to the list. Another way would be to use a txt file. We will encapsulate The Get-Content cmdlet inside of parenthesis so it executes first. It will feed one name at a time to the ComputerName parameter.
PS C:\psworks> Get-WmiObject Win32_Bios -ComputerName (Get-Content Names.txt)
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 0214-6255-9078-8822-9031-3935-43
Version : VRTUAL - 5001223
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 2500-5916-2465-4853-2519-9911-18
Version : VRTUAL - 5001223
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 7563-3642-6655-4653-5455-8957-02
Version : VRTUAL - 5001223
Now we only need to update the txt file when we add or remove a client. Also, we can reuse this list. If you have access to the Active Directory Module, you could just pull the list for AD itself and not have to worry about updating a text file.
PS C:\psworks> Get-WmiObject Win32_Bios -ComputerName ((Get-ADComputer -Filter *).Name)
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 2500-5916-2465-4853-2519-9911-18
Version : VRTUAL - 5001223
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 0214-6255-9078-8822-9031-3935-43
Version : VRTUAL - 5001223
SMBIOSBIOSVersion : 090006
Manufacturer : American Megatrends Inc.
Name : BIOS Date: 05/23/12 17:15:53 Ver: 09.00.06
SerialNumber : 7563-3642-6655-4653-5455-8957-02
Version : VRTUAL - 5001223
Notice that we have 2 pairs on parenthesis. One inside of the other. The inner pair executes the Get-ADComputer –Filter * command. Inside the outer pair, we are simpling dotting out the Name parameter of the resulting three computer objects and feeding them one at a time to the ComputerName parameter.
In Subexpressions
When you display string of information on the screen for an object, odd things can happen. Take a look at this example. This is how a string should look when it is displayed.
PS C:\psworks> "This is a string"
This is a string
In PowerShell, we often work with objects. If you want to display the contents of an object on screen, things can get a bit messy. This first line places the object generated by the cmdlet Get-Host into the variable $PS.
PS C:\psworks> $PS = Get-Host
When we dump the contents of memory to the screen, we get this:
PS C:\psworks> $PS
Name : Windows PowerShell ISE Host
Version : 4.0
InstanceId : 7259e6c3-6dc0-4abe-932a-9fbfe9d3a683
UI : System.Management.Automation.Internal.Host.InternalHostUserI
nterface
CurrentCulture : en-US
CurrentUICulture : en-US
PrivateData : Microsoft.PowerShell.Host.ISE.ISEOptions
IsRunspacePushed : False
Runspace : System.Management.Automation.Runspaces.LocalRunspace
Let’s say we are interested in just the Version property number.
PS C:\psworks> $PS.Version
Major Minor Build Revision
----- ----- ----- --------
4 0 -1 -1
We can see that this is also an object. We want the Major property.
PS C:\psworks> $PS.Version.Major
4
Our goal is to have a string that reads “My version of PowerShell is 4”. Let’s try this without using a subexpression.
PS C:\psworks> "My version of PowerShell is $PS.Version.Major"
My version of PowerShell is System.Management.Automation.Internal.Host.Internal
Host.Version.Major
Not exactly what we want. Whenever you want to display the property information of an object, you need to use a subexpression. A subexpression tells PowerShell to execute what is inside of my parenthesis as if it were code. Our subexpression would look like this $($PS.Version.Major). Let’s take a look at it in our example.
PS C:\psworks> "My version of PowerShell is $($PS.Version.Major)"
My version of PowerShell is 4
Much better.
In a construct
Parenthesis are also used in our scripting constructs. Take a look at this simple IF statement.
$X = 3
If ($X -gt 1) {Write-Host "Greater than 1"}
In this example, the code inside of the parenthesis are being evaluated for True or False. When you see parenthesis in a programming construct, make sure to read the help file for that construct so you know how to properly use the parenthesis. in this case, the help file is About_If.
You will find parenthesis in more complex code of PowerShell, but these cover the most common areas that you will use parenthesis.
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