How to Automate Data-Intensive Tasks in Windows PowerShell

The following excerpt from Windows PowerShell Cookbook, Second Edition shows you how to efficiently run a simple task on large amounts of data.

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One of the major benefits of PowerShell is its capability to automate repetitive tasks. Sometimes these repetitive tasks are action-intensive (such as system maintenance through registry and file cleanup) and consist of complex sequences of commands that will always be invoked together. In those situations, you can write a script to combine these operations to save time and reduce errors.

Other times, you need only to accomplish a single task (for example, retrieving the results of a WMI query) but need to invoke that task repeatedly for a large amount of data. In those situations, PowerShell’s scripting statements, pipeline support, and data management cmdlets help automate those tasks.

If only one piece of data changes (such as a server name or username), store the data in a text file. Use the Get-Content cmdlet to retrieve the items, and then use the Foreach-Object cmdlet (which has the standard aliases foreach and %) to work with each item in that list. Example 2-5 illustrates this technique.

Example 2-5. Using information from a text file to automate data-intensive tasks

PS > Get-Content servers.txt
SERVER1
SERVER2
PS > $computers = Get-Content servers.txt
PS > $computers | Foreach-Object { Get-WmiObject Win32_OperatingSystem -Computer $_ }

SystemDirectory : C:\WINDOWS\system32
Organization    :
BuildNumber     : 2600
Version         : 5.1.2600

SystemDirectory : C:\WINDOWS\system32
Organization    :
BuildNumber     : 2600
Version         : 5.1.2600

If it becomes cumbersome (or unclear) to include the actions in the Foreach-Object cmdlet, you can also use the foreach scripting keyword, as illustrated in Example 2-6.

Example 2-6. Using the foreach scripting keyword to make a looping statement easier to read

$computers = Get-Content servers.txt

foreach($computer in $computers)
{
    ## Get the information about the operating system from WMI
    $system = Get-WmiObject Win32_OperatingSystem -Computer $computer

    ## Determine if it is running Windows XP
    if($system.Version -eq "5.1.2600")
    {
        "$computer is running Windows XP"
    }
}

If several aspects of the data change per task (for example, both the WMI class and the computer name for computers in a large report), create a CSV file with a row for each task. Use the Import-Csv cmdlet to import that data into PowerShell, and then use properties of the resulting objects as multiple sources of related data. Example 2-7 illustrates this technique.

Example 2-7. Using information from a CSV to automate data-intensive tasks

PS > Get-Content WmiReport.csv
ComputerName,Class
LEE-DESK,Win32_OperatingSystem
LEE-DESK,Win32_Bios
PS > $data = Import-Csv WmiReport.csv
PS > $data

ComputerName                          Class
------------                          -----
LEE-DESK                              Win32_OperatingSystem
LEE-DESK                              Win32_Bios


PS > $data |
    Foreach-Object { Get-WmiObject $_.Class -Computer $_.ComputerName }



SystemDirectory : C:\WINDOWS\system32
Organization    :
BuildNumber     : 2600
Version         : 5.1.2600

SMBIOSBIOSVersion : ASUS A7N8X Deluxe ACPI BIOS Rev 1009
Manufacturer      : Phoenix Technologies, LTD
Name              : Phoenix - AwardBIOS v6.00PG
SerialNumber      : xxxxxxxxxxx
Version           : Nvidia - 42302e31

The Import-Csv cmdlet reads a CSV file and, for each row, automatically creates an object with properties that correspond to the names of the columns. Example 2-8 shows the results of a CSV that contains a ComputerName and Class header.

Example 2-8. The Import-Csv cmdlet creating objects with Computer Name and Class properties

PS > $data = Import-Csv WmiReport.csv
PS > $data

ComputerName                         Class
------------                         -----
LEE-DESK                             Win32_OperatingSystem
LEE-DESK                             Win32_Bios


PS > $data[0].ComputerName
LEE-DESK

As the solution illustrates, you can use the Foreach-Object cmdlet to provide data from these objects to repetitive cmdlet calls. It does this by specifying each parameter name, followed by the data (taken from a property of the current CSV object) that applies to it.

While this is the most general solution, many cmdlet parameters can automatically retrieve their value from incoming objects if any property of that object has the same name. This can let you omit the Foreach-Object and property mapping steps altogether. Parameters that support this feature are said to support value from pipeline by property name. The Move-Item cmdlet is one example of a cmdlet with parameters that support this, as shown by the Accept pipeline input rows in Example 2-9.

Example 2-9. Help content of the Move-Item showing a parameter that accepts value from pipeline by property name

PS > Get-Help Move-Item -Full
(...)
PARAMETERS

    -path <string[]>
        Specifies the path to the current location of the items. The default
        is the current directory. Wildcards are permitted.

        Required?                    true
        Position?                    1
        Default value                <current location>
        Accept pipeline input?       true (ByValue, ByPropertyName)
        Accept wildcard characters?  true

    -destination <string>
        Specifies the path to the location where the items are being moved.
        The default is the current directory. Wildcards are permitted, but
        the result must specify a single location.

        To rename the item being moved, specify a new name in the value of
        Destination.

        Required?                    false
        Position?                    2
        Default value                <current location>
        Accept pipeline input?       true (ByPropertyName)
        Accept wildcard characters?  True
        (...)

If you purposefully name the columns in the CSV to correspond to parameters that take their value from pipeline by property name, PowerShell can do some (or all) of the parameter mapping for you. Example 2-10 demonstrates a CSV file that moves items in bulk.

Example 2-10. Using the Import-Csv cmdlet to automate a cmdlet that accepts value from pipeline by property name

PS > Get-Content ItemMoves.csv
Path,Destination
test.txt,Test1Directory
test2.txt,Test2Directory
PS > dir test.txt,test2.txt | Select Name

Name
----
test.txt
test2.txt


PS > Import-Csv ItemMoves.csv | Move-Item
PS > dir Test1Directory | Select Name

Name
----
test.txt


PS > dir Test2Directory | Select Name
Name
----
test2.txt