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Windows PowerShell Pocket Reference, 2nd Edition by Lee Holmes

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A Guided Tour of Windows PowerShell

Introduction

Windows PowerShell promises to revolutionize the world of system management and command-line shells. From its object-based pipelines to its administrator focus to its enormous reach into other Microsoft management technologies, PowerShell drastically improves the productivity of administrators and power users alike.

When you’re learning a new technology, it is natural to feel bewildered at first by all the unfamiliar features and functionality. This perhaps rings especially true for users new to Windows PowerShell because it may be their first experience with a fully featured command-line shell. Or worse, they’ve heard stories of PowerShell’s fantastic integrated scripting capabilities and fear being forced into a world of programming that they’ve actively avoided until now.

Fortunately, these fears are entirely misguided; PowerShell is a shell that both grows with you and grows on you. Let’s take a tour to see what it is capable of:

  • PowerShell works with standard Windows commands and applications. You don’t have to throw away what you already know and use.

  • PowerShell introduces a powerful new type of command. PowerShell commands (called cmdlets) share a common Verb-Noun syntax and offer many usability improvements over standard commands.

  • PowerShell understands objects. Working directly with richly structured objects makes working with (and combining) PowerShell commands immensely easier than working in the plain-text world of traditional shells.

  • PowerShell caters to administrators. Even with all its advances, PowerShell focuses strongly on its use as an interactive shell: the experience of entering commands in a running PowerShell application.

  • PowerShell supports discovery. Using three simple commands, you can learn and discover almost anything PowerShell has to offer.

  • PowerShell enables ubiquitous scripting. With a fully fledged scripting language that works directly from the command line, PowerShell lets you automate tasks with ease.

  • PowerShell bridges many technologies. By letting you work with .NET, COM, WMI, XML, and Active Directory, PowerShell makes working with these previously isolated technologies easier than ever before.

  • PowerShell simplifies management of datastores. Through its provider model, PowerShell lets you manage datastores using the same techniques you already use to manage files and folders.

We’ll explore each of these pillars in this introductory tour of PowerShell. If you are running Windows 7 (or later) or Windows 2008 R2 (or later), PowerShell is already installed. If not, visit the download link to install it. PowerShell and its supporting technologies are together referred to as the Windows Management Framework.

An Interactive Shell

At its core, PowerShell is first and foremost an interactive shell. While it supports scripting and other powerful features, its focus as a shell underpins everything.

Getting started in PowerShell is a simple matter of launching PowerShell.exe rather than cmd.exe—the shells begin to diverge as you explore the intermediate and advanced functionality, but you can be productive in PowerShell immediately.

To launch Windows PowerShell, do one of the following:

  • Click StartAll ProgramsAccessoriesWindows PowerShell

  • Click StartRun, and then type PowerShell

A PowerShell prompt window opens that’s nearly identical to the traditional command prompt window of Windows XP, Windows Server 2003, and their many ancestors. The PS C:\Users\Lee> prompt indicates that PowerShell is ready for input, as shown in Figure 1.

Windows PowerShell, ready for input
Figure 1. Windows PowerShell, ready for input

Once you’ve launched your PowerShell prompt, you can enter DOS-style and Unix-style commands to navigate around the filesystem just as you would with any Windows or Unix command prompt—as in the interactive session shown in Example 1. In this example, we use the pushd, cd, dir, pwd, and popd commands to store the current location, navigate around the filesystem, list items in the current directory, and then return to the original location. Try it!

Example 1. Entering many standard DOS- and Unix-style file manipulation commands produces the same results you get when you use them with any other Windows shell
PS C:\Documents and Settings\Lee> function Prompt { "PS > " }
PS > pushd .
PS > cd \
PS > dir

    Directory: C:\

Mode           LastWriteTime   Length Name
----           -------------   ------ ----
d----    11/2/2006   4:36 AM          $WINDOWS.~BT
d----     5/8/2007   8:37 PM          Blurpark
d----   11/29/2006   2:47 PM          Boot
d----   11/28/2006   2:10 PM          DECCHECK
d----    10/7/2006   4:30 PM          Documents and Settings
d----    5/21/2007   6:02 PM          F&SC-demo
d----     4/2/2007   7:21 PM          Inetpub
d----    5/20/2007   4:59 PM          Program Files
d----    5/21/2007   7:26 PM          temp
d----    5/21/2007   8:55 PM          Windows
-a---     1/7/2006  10:37 PM        0 autoexec.bat
-ar-s   11/29/2006   1:39 PM     8192 BOOTSECT.BAK
-a---     1/7/2006  10:37 PM        0 config.sys
-a---     5/1/2007   8:43 PM    33057 RUU.log
-a---     4/2/2007   7:46 PM     2487 secedit.INTEG.RAW

PS > popd
PS > pwd

Path
----
C:\Documents and Settings\Lee

In this example, our first command customizes the prompt. In cmd.exe, customizing the prompt looks like prompt $P$G. In bash, it looks like PS1="[\h] \w> ". In PowerShell, you define a function that returns whatever you want displayed.

The pushd command is an alternative name (alias) to the much more descriptively named PowerShell command Push-Location. Likewise, the cd, dir, popd, and pwd commands all have more memorable counterparts.

Although navigating around the filesystem is helpful, so is running the tools you know and love, such as ipconfig and notepad. Type the command name and you’ll see results like those shown in Example 2.

Example 2. Windows tools and applications such as ipconfig run in PowerShell just as they do in cmd.exe
PS > ipconfig
Windows IP Configuration


Ethernet adapter Wireless Network Connection 4:

     Connection-specific DNS Suffix .  : hsd1.wa.comcast.net.
     IP Address. . . . . . . . . . . . : 192.168.1.100
     Subnet Mask . . . . . . . . . . . : 255.255.255.0
     Default Gateway . . . . . . . . . : 192.168.1.1
PS > notepad
(notepad launches)

Entering ipconfig displays the IP addresses of your current network connections. Entering notepad runs—as you’d expect—the Notepad editor that ships with Windows. Try them both on your own machine.

Structured Commands (Cmdlets)

In addition to supporting traditional Windows executables, PowerShell introduces a powerful new type of command called a cmdlet (pronounced “command-let”). All cmdlets are named in a Verb-Noun pattern, such as Get-Process, Get-Content, and Stop-Process.

PS > Get-Process -Name lsass
Handles  NPM(K)  PM(K)  WS(K) VM(M) CPU(s)  Id ProcessName
-------  ------  -----  ----- ----- ------  -- -----------
    668      13   6228  1660     46        932 lsass

In this example, you provide a value to the ProcessName parameter to get a specific process by name.

Note

Once you know the handful of common verbs in PowerShell, learning how to work with new nouns becomes much easier. While you may never have worked with a certain object before (such as a Service), the standard Get, Set, Start, and Stop actions still apply. For a list of these common verbs, see Table 10-1 in Chapter 10.

You don’t always have to type these full cmdlet names, however. PowerShell lets you use the Tab key to autocomplete cmdlet names and parameter names:

PS > Get-Pr<TAB> -N<TAB> lsass

For quick interactive use, even that may be too much typing. To help improve your efficiency, PowerShell defines aliases for all common commands and lets you define your own. In addition to alias names, PowerShell requires only that you type enough of the parameter name to disambiguate it from the rest of the parameters in that cmdlet. PowerShell is also case-insensitive. Using the built-in gps alias (which represents the Get-Process cmdlet) along with parameter shortening, you can instead type:

PS > gps -n lsass

Going even further, PowerShell supports positional parameters on cmdlets. Positional parameters let you provide parameter values in a certain position on the command line, rather than having to specify them by name. The Get-Process cmdlet takes a process name as its first positional parameter. This parameter even supports wildcards:

PS > gps l*s

Deep Integration of Objects

PowerShell begins to flex more of its muscle as you explore the way it handles structured data and richly functional objects. For example, the following command generates a simple text string. Since nothing captures that output, PowerShell displays it to you:

PS > "Hello World"
Hello World

The string you just generated is, in fact, a fully functional object from the .NET Framework. For example, you can access its Length property, which tells you how many characters are in the string. To access a property, you place a dot between the object and its property name:

PS > "Hello World".Length
11

All PowerShell commands that produce output generate that output as objects as well. For example, the Get-Process cmdlet generates a System.Diagnostics.Process object, which you can store in a variable. In PowerShell, variable names start with a $ character. If you have an instance of Notepad running, the following command stores a reference to it:

$process = Get-Process notepad

Since this is a fully functional Process object from the .NET Framework, you can call methods on that object to perform actions on it. This command calls the Kill() method, which stops a process. To access a method, you place a dot between the object and its method name:

$process.Kill()

PowerShell supports this functionality more directly through the Stop-Process cmdlet, but this example demonstrates an important point about your ability to interact with these rich objects.

Administrators as First-Class Users

While PowerShell’s support for objects from the .NET Framework quickens the pulse of most users, PowerShell continues to focus strongly on administrative tasks. For example, PowerShell supports MB (for megabyte) and GB (for gigabyte) as some of its standard administrative constants. For example, how many disks will it take to back up a 40 GB hard drive to CD-ROM?

PS > 40GB / 650MB
63.0153846153846

Although the .NET Framework is traditionally a development platform, it contains a wealth of functionality useful for administrators too! In fact, it makes PowerShell a great calendar. For example, is 2008 a leap year? PowerShell can tell you:

PS > [DateTime]::IsLeapYear(2008)
True

Going further, how might you determine how much time remains until summer? The following command converts "06/21/2011" (the start of summer) to a date, and then subtracts the current date from that. It stores the result in the $result variable, and then accesses the TotalDays property.

PS > $result = [DateTime] "06/21/2011" - [DateTime]::Now
PS > $result.TotalDays
283.0549285662616

Composable Commands

Whenever a command generates output, you can use a pipeline character (|) to pass that output directly to another command as input. If the second command understands the objects produced by the first command, it can operate on the results. You can chain together many commands this way, creating powerful compositions out of a few simple operations. For example, the following command gets all items in the Path1 directory and moves them to the Path2 directory:

Get-Item Path1\* | Move-Item -Destination Path2

You can create even more complex commands by adding additional cmdlets to the pipeline. In Example 3, the first command gets all processes running on the system. It passes those to the Where-Object cmdlet, which runs a comparison against each incoming item. In this case, the comparison is $_.Handles -ge 500, which checks whether the Handles property of the current object (represented by the $_ variable) is greater than or equal to 500. For each object in which this comparison holds true, you pass the results to the Sort-Object cmdlet, asking it to sort items by their Handles property. Finally, you pass the objects to the Format-Table cmdlet to generate a table that contains the Handles, Name, and Description of the process.

Example 3. You can build more complex PowerShell commands by using pipelines to link cmdlets, as shown here with Get-Process, Where-Object, Sort-Object, and Format-Table
PS > Get-Process |
    Where-Object { $_.Handles -ge 500 } |
    Sort-Object Handles |
    Format-Table Handles,Name,Description -Auto


Handles Name     Description
------- ----     -----------
    588 winlogon
    592 svchost
    667 lsass
    725 csrss
    742 System
    964 WINWORD  Microsoft Office Word
   1112 OUTLOOK  Microsoft Office Outlook
   2063 svchost

Techniques to Protect You from Yourself

While aliases, wildcards, and composable pipelines are powerful, their use in commands that modify system information can easily be nerve-racking. After all, what does this command do? Think about it, but don’t try it just yet:

PS > gps [b-t]*[c-r] | Stop-Process

It appears to stop all processes that begin with the letters b through t and end with the letters c through r. How can you be sure? Let PowerShell tell you. For commands that modify data, PowerShell supports -WhatIf and -Confirm parameters that let you see what a command would do:

PS > gps [b-t]*[c-r] | Stop-Process -whatif
What if: Performing operation "Stop-Process" on Target 
    "ctfmon (812)".
What if: Performing operation "Stop-Process" on Target
    "Ditto (1916)".
What if: Performing operation "Stop-Process" on Target 
    "dsamain (316)".
What if: Performing operation "Stop-Process" on Target 
    "ehrecvr (1832)".
What if: Performing operation "Stop-Process" on Target 
    "ehSched (1852)".
What if: Performing operation "Stop-Process" on Target 
    "EXCEL (2092)".
What if: Performing operation "Stop-Process" on Target 
    "explorer (1900)".
(...)

In this interaction, using the -WhatIf parameter with the Stop-Process pipelined command lets you preview which processes on your system will be stopped before you actually carry out the operation.

Note that this example is not a dare! In the words of one reviewer:

Not only did it stop everything, but on Vista, it forced a shutdown with only one minute warning!

It was very funny though…At least I had enough time to save everything first!

Common Discovery Commands

While reading through a guided tour is helpful, I find that most learning happens in an ad hoc fashion. To find all commands that match a given wildcard, use the Get-Command cmdlet. For example, by entering the following, you can find out which PowerShell commands (and Windows applications) contain the word process.

PS > Get-Command *process*

CommandType    Name          Definition
-----------    ----          ----------
Cmdlet         Get-Process   Get-Process [[-Name] <Str...
Application    qprocess.exe  c:\windows\system32\qproc...
Cmdlet         Stop-Process  Stop-Process [-Id] <Int32...

To see what a command such as Get-Process does, use the Get-Help cmdlet, like this:

PS > Get-Help Get-Process

Since PowerShell lets you work with objects from the .NET Framework, it provides the Get-Member cmdlet to retrieve information about the properties and methods that an object, such as a .NET System.String, supports. Piping a string to the Get-Member command displays its type name and its members:

PS > "Hello World" | Get-Member

   TypeName: System.String

Name        MemberType  Definition
----        ----------  ----------
(...)
PadLeft     Method      System.String PadLeft(Int32 tota...
PadRight    Method      System.String PadRight(Int32 tot...
Remove      Method      System.String Remove(Int32 start...
Replace     Method      System.String Replace(Char oldCh...
Split       Method      System.String[] Split(Params Cha...
StartsWith  Method      System.Boolean StartsWith(String...
Substring   Method      System.String Substring(Int32 st...
ToCharArray Method      System.Char[] ToCharArray(), Sys...
ToLower     Method      System.String ToLower(), System....
ToLower-
Invariant   Method      System.String ToLowerInvariant()
ToString    Method      System.String ToString(), System...
ToUpper     Method      System.String ToUpper(), System....
ToUpper-
Invariant   Method      System.String ToUpperInvariant()
Trim        Method      System.String Trim(Params Char[]...
TrimEnd     Method      System.String TrimEnd(Params Cha...
TrimStart   Method      System.String TrimStart(Params C...
Chars       Parameter-  System.Char Chars(Int32 index) {...
            izedProperty
Length      Property    System.Int32 Length {get;}

Ubiquitous Scripting

PowerShell makes no distinction between the commands typed at the command line and the commands written in a script. Your favorite cmdlets work in scripts and your favorite scripting techniques (e.g., the foreach statement) work directly on the command line. For example, to add up the handle count for all running processes:

PS > $handleCount = 0
PS > foreach($process in Get-Process) { $handleCount +=
    $process.Handles }
PS > $handleCount
19403

While PowerShell provides a command (Measure-Object) to measure statistics about collections, this short example shows how PowerShell lets you apply techniques that normally require a separate scripting or programming language.

In addition to using PowerShell scripting keywords, you can also create and work directly with objects from the .NET Framework that you may be familiar with. PowerShell becomes almost like the C# immediate mode in Visual Studio. Example 4 shows how PowerShell lets you easily interact with the .NET Framework.

Example 4. Using objects from the .NET Framework to retrieve a web page and process its content
PS > $webClient = New-Object System.Net.WebClient
PS > $content = $webClient.DownloadString("http://blogs.msdn.
    com/PowerShell/rss.aspx")
PS > $content.Substring(0,1000)
<?xml version="1.0" encoding="UTF-8" ?>
<?xml-stylesheet type="text/xsl" href="http://blogs.msdn.com/
    utility/FeedS
tylesheets/rss.xsl" media="screen"?><rss version="2.0" xmlns:
    dc="http://pu
rl.org/dc/elements/1.1/" xmlns:slash="http://purl.org/rss/1.0/
    modules/slas
h/" xmlns:wfw="http://wellformedweb.org/CommentAPI/"><channel>
<title>Windo
(...)

Ad Hoc Development

By blurring the lines between interactive administration and writing scripts, the history buffers of PowerShell sessions quickly become the basis for ad hoc script development. In this example, you call the Get-History cmdlet to retrieve the history of your session. For each item, you get its CommandLine property (the thing you typed) and send the output to a new script file.

PS > Get-History | Foreach-Object { $_.CommandLine } > c:
    \temp\script.ps1
PS > notepad c:\temp\script.ps1
(save the content you want to keep)
PS > c:\temp\script.ps1

Note

If this is the first time you’ve run a script in PowerShell, you will need to configure your execution policy. For more information about selecting an execution policy, type help about_signing.

.

Bridging Technologies

We’ve seen how PowerShell lets you fully leverage the .NET Framework in your tasks, but its support for common technologies stretches even further. As Example 5 (continued from Example 4) shows, PowerShell supports XML.

Example 5. Working with XML content in PowerShell
PS > $xmlContent = [xml] $content
PS > $xmlContent

xml                       xml-stylesheet            rss
---                       --------------            ---
version="1.0" encoding... type="text/xsl" href="... rss

PS > $xmlContent.rss

version : 2.0
dc      : http://purl.org/dc/elements/1.1/
slash   : http://purl.org/rss/1.0/modules/slash/
wfw     : http://wellformedweb.org/CommentAPI/
channel : channel

PS > $xmlContent.rss.channel.item | select Title

title
-----
CMD.exe compatibility
Time Stamping Log Files
Microsoft Compute Cluster now has a PowerShell Provider and 
    Cmdlets
The Virtuous Cycle: .NET Developers using PowerShell
(...)

PowerShell also lets you work with Windows Management Instrumentation (WMI) and CIM:

PS > Get-CimInstance Win32_Bios

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

Or, as Example 6 shows, you can work with Active Directory Service Interfaces (ADSI).

Example 6. Working with Active Directory in PowerShell
PS > [ADSI] "WinNT://./Administrator" | Format-List *

UserFlags                  : {66113}
MaxStorage                 : {-1}
PasswordAge                : {19550795}
PasswordExpired            : {0}
LoginHours                 : {255 255 255 255 255 255 255 255
                             255 255 255 255 255 255 255 255 
                             255 255 255 255 255}
FullName                   : {}
Description                : {Built-in account for 
                             administering the computer/
                             domain}
BadPasswordAttempts        : {0}
LastLogin                  : {5/21/2007 3:00:00 AM}
HomeDirectory              : {}
LoginScript                : {}
Profile                    : {}
HomeDirDrive               : {}
Parameters                 : {}
PrimaryGroupID             : {513}
Name                       : {Administrator}
MinPasswordLength          : {0}
MaxPasswordAge             : {3710851}
MinPasswordAge             : {0}
PasswordHistoryLength      : {0}
AutoUnlockInterval         : {1800}
LockoutObservationInterval : {1800}
MaxBadPasswordsAllowed     : {0}
RasPermissions             : {1}
objectSid                  : {1 5 0 0 0 0 0 5 21 0 0 0 121 227
                             252 83 122 130 50 34 67 23 10 50 
                             244 1 0 0}

Or, as Example 7 shows, you can even use PowerShell for scripting traditional COM objects.

Example 7. Working with COM objects in PowerShell
PS > $firewall = New-Object -com HNetCfg.FwMgr
PS > $firewall.LocalPolicy.CurrentProfile

Type                      : 1
FirewallEnabled           : True
ExceptionsNotAllowed      : False
NotificationsDisabled     : False
UnicastResponsesToMulti-  
castBroadcastDisabled     : False
RemoteAdminSettings       : System.__ComObject
IcmpSettings              : System.__ComObject
GloballyOpenPorts         : {Media Center Extender Serv
                            ice, Remote Media Center Ex
                            perience, Adam Test Instanc
                            e, QWAVE...}
Services                  : {File and Printer Sharing,
                            UPnP Framework, Remote Desk
                            top}
AuthorizedApplications    : {Remote Assistance, Windows
                            Messenger, Media Center,
                            Trillian...} 

Namespace Navigation Through Providers

Another avenue PowerShell offers for working with the system is providers. PowerShell providers let you navigate and manage data stores using the same techniques you already use to work with the filesystem, as illustrated in Example 8.

Example 8. Navigating the filesystem
PS > Set-Location c:\
PS > Get-ChildItem

    Directory: C:\

Mode                LastWriteTime     Length Name
----                -------------     ------ ----
d----         11/2/2006   4:36 AM            $WINDOWS.~BT
d----          5/8/2007   8:37 PM            Blurpark 
d----        11/29/2006   2:47 PM            Boot
d----        11/28/2006   2:10 PM            DECCHECK
d----         10/7/2006   4:30 PM            Documents and 
                                             Settings
d----         5/21/2007   6:02 PM            F&SC-demo
d----          4/2/2007   7:21 PM            Inetpub
d----         5/20/2007   4:59 PM            Program Files
d----         5/21/2007  11:47 PM            temp
d----         5/21/2007   8:55 PM            Windows
-a---          1/7/2006  10:37 PM          0 autoexec.bat
-ar-s        11/29/2006   1:39 PM       8192 BOOTSECT.BAK
-a---          1/7/2006  10:37 PM          0 config.sys
-a---          5/1/2007   8:43 PM      33057 RUU.log
-a---          4/2/2007   7:46 PM       2487 secedit.INTEG.RAW

This also works on the registry, as shown in Example 9.

Example 9. Navigating the registry
PS > Set-Location HKCU:\Software\Microsoft\Windows\
PS > Get-ChildItem

   Hive: HKEY_CURRENT_USER\Software\Microsoft\Windows

SKC VC Name                            Property
--- -- ----                            --------
 30  1 CurrentVersion                  {ISC}
  3  1 Shell                           {BagMRU Size}
  4  2 ShellNoRoam                     {(default), BagMRU Size}

PS > Set-Location CurrentVersion\Run
PS > Get-ItemProperty .

(...)
FolderShare           : "C:\Program Files\FolderShare\
                        FolderShare.exe" /background
TaskSwitchXP          : d:\lee\tools\TaskSwitchXP.exe
ctfmon.exe            : C:\WINDOWS\system32\ctfmon.exe
Ditto                 : C:\Program Files\Ditto\Ditto.exe
(...)

And it even works on the machine’s certificate store, as Example 10 illustrates.

Example 10. Navigating the certificate store
PS > Set-Location cert:\CurrentUser\Root
PS > Get-ChildItem

    Directory: Microsoft.PowerShell.Security\
        Certificate::CurrentUser\Root


Thumbprint                                Subject
----------                                -------
CDD4EEAE6000AC7F40C3802C171E30148030C072  CN=Microsoft Root 
                                          Certificate...
BE36A4562FB2EE05DBB3D32323ADF445084ED656  CN=Thawte 
                                          Timestamping CA, 
                                          OU...
A43489159A520F0D93D032CCAF37E7FE20A8B419  CN=Microsoft Root
                                          Authority, ...
9FE47B4D05D46E8066BAB1D1BFC9E48F1DBE6B26  CN=PowerShell Local
                                          Certifica...
7F88CD7223F3C813818C994614A89C99FA3B5247  CN=Microsoft 
                                          Authenticode(tm)...
245C97DF7514E7CF2DF8BE72AE957B9E04741E85  OU=Copyright (c)
                                          1997 Microso...
(...)

Much, Much More

As exciting as this guided tour was, it barely scratches the surface of how you can use PowerShell to improve your productivity and systems management skills. For more information about getting started in PowerShell, see the “Getting Started” and “User Guide” files included in the Windows PowerShell section of your Start menu. For a cookbook-style guide to PowerShell (and hard-won solutions to its most common problems), you may be interested in the source of the material in this pocket reference: my book Windows PowerShell Cookbook, 3rd Edition (O’Reilly).

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