PowerShell is a powerful tool that enables
administrators to manage Windows platform applications and to complete
automation tasks. This section sheds some light on how PowerShell’s many
uses can be discovered and how it can be used to manage Windows Server
2008 R2.
Exploring PowerShell
Before
using PowerShell, you might want to become more familiar with its
cmdlets and features. To assist administrators with exploring
PowerShell, the PowerShell team decided to do two things. First, they
included a cmdlet that functions very similarly to how the UNIX man
pages function. Second, they also included a cmdlet that returns
information about commands available in the current session. Together,
these cmdlets allow a novice to tap into and understand PowerShell
without secondary reference materials; explanations of these cmdlets are
discussed in the following sections.
Getting Help
The Get-Help cmdlet is used to
retrieve help information about cmdlets, aliases, and from help files.
To display a list of all help topics this cmdlet supports, enter
Get-Help * at the PowerShell command prompt, as shown here:
PS C:\> get-help *
Name Category Synopsis
---- -------- --------
ac Alias Add-Content
asnp Alias Add-PSSnapin
clc Alias Clear-Content
cli Alias Clear-Item
clp Alias Clear-ItemProperty
clv Alias Clear-Variable
cpi Alias Copy-Item
cpp Alias Copy-ItemProperty
cvpa Alias Convert-Path
...
If that list seems too large
to work with, it can be shortened by filtering on topic name and
category. For example, to get a list of all cmdlets starting with the
verb Get, try the command shown in the following example:
PS C:\> get-help -Name get-* -Category cmdlet
Name Category Synopsis
---- -------- --------
Get-Command Cmdlet Gets basic information...
Get-Help Cmdlet Displays information a...
Get-History Cmdlet Gets a list of the com...
Get-PSSnapin Cmdlet Gets the Windows Power...
Get-EventLog Cmdlet Gets information about...
Get-ChildItem Cmdlet Gets the items and chi...
Get-Content Cmdlet Gets the content of th...
...
PS C:\>
After
selecting a help topic, that topic can be retrieved by using the topic
name as the parameter to the Get-Help cmdlet. For example, to retrieve
help for the Get-Content cmdlet, enter the following command:
PS C:\> get-help get-content
After executing this
command, a shortened view of the help content for the Get-Content cmdlet
is displayed. To view the full help content, include the full switch
parameter with the command:
PS C:\> get-help get-content –full
After executing the command
with the full switch parameter, you will find that the full help
content is divided into several sections. Table 1 describes each of these sections.
Table 1. PowerShell Help Sections
| Help Section | Description |
|---|
| Name | The name of the cmdlet |
| Synopsis | A brief description of what the cmdlet does |
| Description | A detailed description of the cmdlet’s behavior, usually including usage examples |
| Syntax | Specific usage details for entering commands with the cmdlet |
| Parameters | Valid parameters that can be used with this cmdlet |
| Inputs | The type of input this cmdlet accepts |
| Outputs | The type of data that the cmdlet returns |
| Notes | Additional detailed information on using the cmdlet, including specific scenarios and possible limitations or idiosyncrasies |
| Examples | Common usage examples for the cmdlet |
| Related Links | References other cmdlets that perform similar tasks |
Get-Command
The Get-Command is used to
gather basic information about cmdlets and other commands that are
available. For example, when executed, the Get-Command lists all the
cmdlets available to the PowerShell session:
PS C:\> get-command
CommandType Name Definition
----------- ---- ----------
Cmdlet Add-Content Add-Content [-Path] <String[...
Cmdlet Add-History Add-History [[-InputObject] ...
Cmdlet Add-Member Add-Member [-MemberType] <PS...
Cmdlet Add-PSSnapin Add-PSSnapin [-Name] <String...
Cmdlet Clear-Content Clear-Content [-Path] <Strin...
Cmdlet Clear-Item Clear-Item [-Path] <String[]...
Cmdlet Clear-ItemProperty Clear-ItemProperty [-Path] <...
Cmdlet Clear-Variable Clear-Variable [-Name] <Stri...
Cmdlet Compare-Object Compare-Object [-ReferenceOb...
...
PS C:\>
Next, to retrieve
basic information about a particular cmdlet, you would then include that
cmdlet’s name and argument. For example:
PS C:\> Get-Command Get-Process
CommandType Name Definition
----------- ---- ----------
Cmdlet Get-Process Get-Process [[-Name] <String...
PS C:\>
The Get-Command cmdlet is
more powerful than Get-Help because it lists all available commands
(cmdlets, scripts, aliases, functions, and native applications) in a
PowerShell session, as shown in this example:
PS C:\> get-command note*
CommandType Name Definition
----------- ---- ----------
Application NOTEPAD.EXE C:\WINDOWS\NOTEPAD.EXE
Application notepad.exe C:\WINDOWS\system32\notepad.exe
PS C:\>
When using Get-Command with
elements other than cmdlets, the information returned is a little
different from information you see for a cmdlet. For example, with an
existing application,
the value of the Definition property is the path to the application.
However, other information about the application is also available, as
shown here:
PS C:\> get-command ipconfig | format-list *
FileVersionInfo : File: C:\WINDOWS\system32\ipconfig.exe
InternalName: ipconfig.exe
OriginalFilename: ipconfig.exe
FileVersion: 5.1.2600.2180 (xpsp_sp2_rtm.040803-2158)
FileDescription: IP Configuration Utility
Product: Microsoftr Windowsr Operating System
ProductVersion: 5.1.2600.2180
Debug: False
Patched: False
PreRelease: False
PrivateBuild: False
SpecialBuild: False
Language: English (United States)
Path : C:\WINDOWS\system32\ipconfig.exe
Extension : .exe
Definition : C:\WINDOWS\system32\ipconfig.exe
Name : ipconfig.exe
CommandType : Application
With a function, the Definition property is the body of the function:
PS C:\> get-command Prompt
CommandType Name Definition
----------- ---- ----------
Function prompt Write-Host ("PS" + $(Get-Lo...
PS C:\>
With an alias, the Definition property is the aliased command:
PS C:\> get-command write
CommandType Name Definition
----------- ---- ----------
Alias write Write-Output
PS C:\>
With a script file, the Definition property is the path to the script. With a non-PowerShell script (such as a .bat or .vbs file), the information returned is the same as other existing applications.
Managing Services
In PowerShell, a number of cmdlets can be used to manage services on a local machine. A list of these cmdlets is as follows:
Get-Service— Used to gather service information from Windows.
New-Service— Used to create a new service in Windows.
Restart-Service— Used to restart services.
Resume-Service— Used to resume suspended services.
Set-Service— Used to modify service configurations.
Start-Service— Used to start services.
Stop-Service— Used to stop services.
Suspend-Service— Used to suspend services.
Getting Service Information
When the Get-Service cmdlet
is executed, it returns a collection of objects that contains
information about all the services that are present on a Windows system.
A representation of that object collection is then outputted into a
formatted table, as shown in the following example:
PS C:\> get-service
Status Name DisplayName
------ ---- -----------
Running AeLookupSvc Application Experience
Stopped ALG Application Layer Gateway Service
Running AppHostSvc Application Host Helper Service
Stopped Appinfo Application Information
Stopped AppMgmt Application Management
Stopped aspnet_state ASP.NET State Service
Stopped AudioEndpointBu... Windows Audio Endpoint Builder
Stopped AudioSrv Windows Audio
...
To filter the information
returned based on the service status, the object collection can be piped
to the Where-Object cmdlet, as shown in the following example:
PS C:\> get-service | where-object {$_.Status -eq "Stopped"}
Status Name DisplayName
------ ---- -----------
Stopped ALG Application Layer Gateway Service
Stopped Appinfo Application Information
Stopped AppMgmt Application Management
Stopped aspnet_state ASP.NET State Service
Stopped AudioEndpointBu... Windows Audio Endpoint Builder
Stopped AudioSrv Windows Audio
...
As
shown in the preceding example, the Where-Object object cmdlet is used
in conjunction with a code block {...}, which is executed as the filter.
In this case, the code block contained an expression that filtered the
object collection based on services that were “Stopped.” The same type
of logic can also be applied to return information about a particular
service. For example:
PS C:\> get-service | where-object {$_.Name -eq "DNS"} | fl
Name : DNS
DisplayName : DNS Server
Status : Running
DependentServices : {}
ServicesDependedOn : {Afd, Tcpip, RpcSs, NTDS}
CanPauseAndContinue : True
CanShutdown : True
CanStop : True
ServiceType : Win32OwnProcess
PS C:\>
In the preceding
example, the object collection from the Get-Service cmdlet is piped to
the Where-Object cmdlet. The filter statement defined script block then
instructs the Where-Object cmdlet to return an object for the DNS
service. The object that is returned by this cmdlet is then piped to the
Format-List cmdlet, which writes a formatted list (containing
information about the object) back to the console session.
Note
A shorter method for performing the preceding action is to use the name switch, as shown in the following command: get-service –name DNS.
Managing Service Statuses
To stop a service in PowerShell, the Stop-Service cmdlet is used, as shown in this example:
PS C:\> stop-service -name dns
Notice
that when the cmdlet has finished executing, no status information
about the service’s status is returned. To gather that information, the
passthru switch parameter can be used to pass the object created by a
cmdlet through to the pipeline. For example:
PS C:\> start-service -name dns -pass | ft
Status Name DisplayName
------ ---- -----------
Running DNS DNS Server
In the preceding example,
the passthru switch parameter is used in conjunction with the
Start-Service cmdlet. When the cmdlet has finished executing, thus
starting the DNS service, the object is piped to the Format-Table
cmdlet, which then displays status information about the DNS service.
Modifying Services
The Set-Service cmdlet is
used to change a service’s properties (such as its description, display
name, and start mode). To use this cmdlet, either pass it a service
object or specify the name of the service to be modified, plus the
property to be modified. For example, to modify the startup type of the
DNS service, use the following command:
PS C:\> set-service -name DNS -start "manual"
A startup type can be
defined as Automatic, Manual, or Disabled. To change a service’s
description, a command might look as follows:
PS C:\> set-service -name DNS -description "My Important DNS Service"
Note
The service management
cmdlets in PowerShell are not end-alls for managing Windows services.
There are a number of areas in which these cmdlets are lacking—for
example, not being able to define a service’s logon account or report on
its startup type. Luckily, if a more in-depth interface is needed, an
administrator can always fall back onto WMI.
