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This chapter is from the book

This chapter is from the book

Understanding Providers

Most computer systems are used to store data, often in a structure such as a file system. Because of the amount of data stored in these structures, processing and finding information can be unwieldy. Most shells have interfaces, or providers, for interacting with data stores in a predictable, set manner. PowerShell also has a set of providers for presenting the contents of data stores through a core set of cmdlets. You can then use these cmdlets to browse, navigate, and manipulate data from stores through a common interface. To get a list of the core cmdlets, use the following command:

PS C:\> help about_core_commands
...
    ChildItem CMDLETS
    Get-ChildItem

    CONTENT CMDLETS
    Add-Content
    Clear-Content
    Get-Content
    Set-Content

    DRIVE CMDLETS
    Get-PSDrive
    New-PSDrive
    Remove-PSDrive

    ITEM CMDLETS
    Clear-Item
    Copy-Item
    Get-Item
    Invoke-Item
    Move-Item
    New-Item
    Remove-Item
    Rename-Item
    Set-Item

    LOCATION CMDLETS
    Get-Location
    Pop-Location
    Push-Location
    Set-Location

    PATH CMDLETS
    Join-Path
    Convert-Path
    Split-Path
    Resolve-Path
    Test-Path

    PROPERTY CMDLETS
    Clear-ItemProperty
    Copy-ItemProperty
    Get-ItemProperty
    Move-ItemProperty
    New-ItemProperty
    Remove-ItemProperty
    Rename-ItemProperty
    Set-ItemProperty

    PROVIDER CMDLETS
    Get-PSProvider



PS C:\>
               

To view built-in PowerShell providers, use the following command:

PS C:\> get-psprovider

Name                 Capabilities                  Drives
----                 ------------                  ------
Alias                ShouldProcess                 {Alias}
Environment          ShouldProcess                 {Env}
FileSystem           Filter, ShouldProcess         {C, D, E, F...}
Function             ShouldProcess                 {Function}
Registry             ShouldProcess                 {HKLM, HKCU}
Variable             ShouldProcess                 {Variable}
Certificate          ShouldProcess                 {cert}



PS C:\>

The preceding list displays not only built-in providers, but also the drives each provider currently supports. A drive is an entity that a provider uses to represent a data store through which data is made available to the PowerShell session. For example, the Registry provider creates a PowerShell drive for the HKEY_LOCAL_MACHINE and HKEY_CURRENT_USER Registry hives.

To see a list of all current PowerShell drives, use the following command:

PS C:\> get-psdrive

Name       Provider      Root
----       --------      ----
Alias      Alias
C          FileSystem    C:cert       Certificate   D          FileSystem    D:E          FileSystem    E:Env        Environment
F          FileSystem    F:Function   Function
G          FileSystem    G:HKCU       Registry      HKEY_CURRENT_USER
HKLM       Registry      HKEY_LOCAL_MACHINE
U          FileSystem    U
Variable   Variable



PS C:\>
               

Accessing Drives and Data

One way to access PowerShell drives and their data is with the Set-Location cmdlet. This cmdlet, shown in the following example, changes the working location to another specified location that can be a directory, subdirectory, location stack, or Registry location:

PS C:\> set-location hklm:
PS HKLM:\> set-location software\microsoft\windows
PS HKLM:\software\microsoft\windows>

Next, use the Get-ChildItem cmdlet to list the subkeys under the Windows key:

PS HKLM:\software\microsoft\windows> get-childitem



   Hive: Microsoft.PowerShell.Core\Registry::HKEY_LOCAL_MACHINE\software\micros
oft\windows

SKC  VC Name                           Property
---  -- ----                           --------
 55  13 CurrentVersion                 {DevicePath, MediaPathUnexpanded, SM_...
  0  16 Help                           {PINTLPAD.HLP, PINTLPAE.HLP, IMEPADEN...
  0  36 Html Help                      {PINTLGNE.CHM, PINTLGNT.CHM, PINTLPAD...
  1   0 ITStorage                      {}
  0   0 Shell                          {}


PS HKLM:\software\microsoft\windows>
               

Note that with a Registry drive, the Get-ChildItem cmdlet lists only the subkeys under a key, not the actual Registry values. This is because Registry values are treated as properties for a key rather than a valid item. To retrieve these values from the Registry, you use the Get-ItemProperty cmdlet, as shown in this example:

PS HKLM:\software\microsoft\windows> get-itemproperty currentversion



PSPath                   : Microsoft.PowerShell.Core\Registry::HKEY_LOCAL_MACHI
                           NE\software\microsoft\windows\currentversion
PSParentPath             : Microsoft.PowerShell.Core\Registry::HKEY_LOCAL_MACHI
                           NE\software\microsoft\windows
PSChildName              : currentversion
PSDrive                  : HKLM
PSProvider               : Microsoft.PowerShell.Core\Registry
DevicePath               : C:\WINDOWS\inf
MediaPathUnexpanded      : C:\WINDOWS\Media
SM_GamesName             : Games
SM_ConfigureProgramsName : Set Program Access and Defaults
ProgramFilesDir          : C:\Program Files
CommonFilesDir           : C:\Program Files\Common Files
ProductId                : 76487-OEM-0011903-00101
WallPaperDir             : C:\WINDOWS\Web\Wallpaper
MediaPath                : C:\WINDOWS\Media
ProgramFilesPath         : C:\Program Files
SM_AccessoriesName       : Accessories
PF_AccessoriesName       : Accessories
(default)                :



PS HKLM:\software\microsoft\windows>

As with the Get-Process command, the data returned is a collection of objects. You can modify these objects further to produce the output you want, as this example shows:

PS HKLM:\software\microsoft\windows> get-itemproperty currentversion |
select ProductId

ProductId
---------
76487-OEM-XXXXXXX-XXXXX


PS HKLM:\software\microsoft\windows>

Accessing data from a FileSystem drive is just as simple. The same type of command logic is used to change the location and display the structure:

PS HKLM:\software\microsoft\windows> set-location c:
PS C:\> set-location "C:\WINDOWS\system32\windowspowershell\v1.0"
PS C:\WINDOWS\system32\windowspowershell\v1.0> get-childitem about_a*


    Directory: Microsoft.PowerShell.Core\FileSystem::C:\WINDOWS\system32\window
    spowershell\v1.0


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
-----          9/8/2006   2:10 AM       5662 about_alias.help.txt
-----          9/8/2006   2:10 AM       3504 about_arithmetic_operators.help.txt
-----          9/8/2006   2:10 AM       8071 about_array.help.txt
-----          9/8/2006   2:10 AM      15137 about_assignment_operators.help.txt
-----          9/8/2006   2:10 AM       5622 about_associative_array.help.txt
-----          9/8/2006   2:10 AM       3907 about_automatic_variables.help.txt
...



PS C:\WINDOWS\system32\windowspowershell\v1.0>

What's different is that data is stored in an item instead of being a property of that item. To retrieve data from an item, use the Get-Content cmdlet, as shown in this example:

PS C:\WINDOWS\system32\windowspowershell\v1.0> get-content
about_Alias.help.txt
TOPIC
    Aliases

SHORT DESCRIPTION
    Using pseudonyms to refer to cmdlet names in the Windows PowerShell

LONG DESCRIPTION
    An alias is a pseudonym, or "nickname," that you can assign to a
    cmdlet so that you can use the alias in place of the cmdlet name.
    The Windows PowerShell interprets the alias as though you had
    entered the actual cmdlet name. For example, suppose that you want
    to retrieve today's date for the year 1905. Without an alias, you
    would use the following command:

        Get-Date -year 1905
...



PS C:\WINDOWS\system32\windowspowershell\v1.0>

Mounting a Drive

PowerShell drives can be created and removed, which is handy when you're working with a location or set of locations frequently. Instead of having to change the location or use an absolute path, you can create new drives (also referred to as "mounting a drive" in PowerShell) as shortcuts to those locations. To do this, use the New-PSDrive cmdlet, shown in the following example:

PS C:\> new-psdrive -name PSScripts -root D:\Dev\Scripts -psp FileSystem


Name       Provider      Root                                   CurrentLocation
----       --------      ----                                   ---------------
PSScripts  FileSystem    D:\Dev\Scripts



PS C:\> get-psdrive


Name       Provider      Root                                   CurrentLocation
----       --------      ----                                   ---------------
Alias      Alias
C          FileSystem    C:cert       Certificate   D          FileSystem    D:E          FileSystem    E:Env        Environment
F          FileSystem    F:Function   Function
G          FileSystem    G:HKCU       Registry      HKEY_CURRENT_USER                             software
HKLM       Registry      HKEY_LOCAL_MACHINE                  ...crosoft\windows
PSScripts  FileSystem    D:\Dev\Scripts
U          FileSystem    U:Variable   Variable



PS C:\>

To remove a drive, use the Remove-PSDrive cmdlet, as shown here:

PS C:\> remove-psdrive -name PSScripts
PS C:\> get-psdrive


Name       Provider      Root                       CurrentLocation
----       --------      ----                       ---------------
Alias      Alias
C          FileSystem    C:cert       Certificate   D          FileSystem    D:E          FileSystem    E:Env        Environment
F          FileSystem    F:Function   Function
G          FileSystem    G:HKCU       Registry      HKEY_CURRENT_USER          software
HKLM       Registry      HKEY_LOCAL_MACHINE         ...crosoft\windows
U          FileSystem    U:Variable   Variable



PS C:\>
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