Automate Data-Intensive Tasks

1. Problem

You want to invoke a simple task on large amounts of data.

2. Solution

If only one piece of data changes (such as a server name or user name), 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

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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 by 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








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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


 


 


                                        


 








3. Discussion


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.


One of the options given by the solution is the Import-Csv cmdlet. 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 >


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 byspecifying 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 anyproperty of that object has the same name. This can let you to 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








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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 propertyname, 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











For more information about the Foreach-Object cmdlet and foreach scripting keyword, see Section 2.4, “Work with Each Item in a List or Command Output.” For more information about working with CSV files, see Section 8.6, “Import Structured Data from a CSV File.” For more information about working with Windows Management Instrumentation (WMI), see Section 15.1, “Access Windows Management Instrumentation Data.”

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				July 17th, 2008 | administration,  power shell,  server,  windows