Powershell is a command line interface for Windows that offers a very powerful and flexible model.
It is now a feature included with Windows 7 and Windows Server 2008 R2, not an optional download as before.
In this post, I show some sample commands that can help you understand some of the basic features and a few more complex ones. 

If you never played with it before, try running Get-Help and Get-Command in a PowerShell prompt.

Shows a list of commands: Get-Command
Shows the help overview: Get-Help
Show the help for “Dir”: Get-Help Dir

Let's use the Dir command now (actually an alias for Get-ChildItem) and a number of ways to transform the output using pipeline functions:

Shows Directory: Dir
Shows Directory in list format (two ways): Dir | Format-List
Dir | FL
Shows Directory sorted by file length: Dir | Sort Length
Shows Directory sorted by file length in descending order: Dir | Sort Length –Descending
Shows all the methods and properties for the objects resulting from Dir (files and folders): Dir | Get-Member
Shows a selected list of properties instead of the default list: Dir | Select  Directory, Name, Extension, Length
Shows directory in HTML format (not much use going to the console like this, though): Dir | ConvertTo-Html
Output the Directory listing to a file: Dir | Out-File psfilelist.txt
Output the Directory listing to a grid in window: Dir | Out-GridView
All together now: Shows selected list of properties, sorted, in HTML, going to a file. You need to open the file yourself: Dir | Select Directory, Name, Extension, Length | Sort Length -Descending | ConvertTo-Html | Out-File psfilelist.htm

Now exploring other “drives” in PowerShell with Get-PSDrive, including the certificate store and the registry.

Get list of PowerShell “drives”: Get-PSDrive
Shows environment variables: Dir ENV:\
Shows the certiticate store: Dir CERT:\
Shows root certificates for the machine: Dir CERT:\LocalMachine\Root | Select FriendlyName, NotAfter
Shows “HK Local Machine” portion of the registry Dir HKLM:
Shows specified part of the registry: Dir HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion

Another easy way to get interesting data is with Get-Process.

List running processes: Get-Process
Shows all the methods and properties for the process objects: Get-Process | Get-Member
Shows selected list of properties of running processes, formatted as table: Get-Process | Select Id, Name, Product, CPU, WorkingSet | Format-Table –autosize

Combining PowerShell with WMI is also very interesting. You can leverage any WMI provider on the box using Get-WmiObject.
You can get a list of WMI Classes from http://msdn.microsoft.com/en-us/library/aa394554(VS.85).aspx

Shows all WMI objects with "disk" on the name: Get-WmiObject -List *disk* | Select Name
Shows disk partitions: Get-WmiObject Win32_DiskPartition | Select Name, Size, BootPartition
Shows logical disks: Get-WmiObject Win32_LogicalDisk | Select DeviceID, DriveType, Size, FreeSpace
Shows mapped drives (with NET USE command): Get-WmiObject Win32_MappedLogicalDisk | Select Name, ProviderName, FileSystem, Size, FreeSpace | Format-Table

PowerShell also lets you call the .NET Framework, which is a huge library.
You need to use a syntax where the full class name (library.class) is mentioned in [], followed by a :: and the method name.

You can find a reference for it at http://msdn.microsoft.com/en-us/library/ms229335.aspx

Shows network interfaces: [System.Net.NetworkInformation.NetworkInterface]::GetAllNetworkInterfaces() | Select Name, Speed, OperationalStatus
Shows identity of the current logged user: [System.Security.Principal.WindowsIdentity]::GetCurrent() | Select Name, AuthenticationType, IsAuthenticated, IsSystem
Shows drive information: [System.IO.DriveInfo]::GetDrives() | Select Name, DriveType, IsReady, TotalSize, TotalFreeSpace, RootDirectory | Format-Table -autosize

It’s also interesting to iterate through the list of resulting objects, to perform additional actions.
You use the ForEach keyword (actually an alias for ForEach-Object), which allows you to run something for each item. The item is referred to as $_.
You can also use the symbol % instead of ForEach-Object.

Change to the application data folder, which is obtained from the environment variables: Dir Env:\AppData | ForEach { CD $_.Value }
Dir Env:\AppData | % { CD $_.Value }
Show all text files enumerated by the Dir command: Dir *.TXT | ForEach { Type $_ }
Dir *.TXT | % { Type $_ }
Show root directory for all drives enumerated by GetDrives: [System.IO.DriveInfo]::GetDrives() | foreach { Dir $_ }
[System.IO.DriveInfo]::GetDrives() | % { Dir $_ }

A similar syntax is used for Where (actually an alias for Where-Object), which can be used to filter objects in the pipeline.
You can also use the symbol ? instead of Where-Object.

Show selected properties of processes using more than 10MB of memory, in descending order, formatted as table: Get-Process | Select Id, Name, Product, CPU, WorkingSet | Where { $_.WorkingSet -gt 10*1024*1024} | Sort WorkingSet -Descending | Format-Table –autosize
Shows all services that are stopped: Get-Service | Where { $_.Status -eq "Stopped" }
Get-Service | ? { $_.Status -eq "Stopped" }

Now let's focus on the DFS Namespaces service, which is something I’m working on (these will only work if the box is a Windows Server file server with the DFS-N role service installed):

Shows all 2000 mode domain namespaces on the current computer, using the registry: Dir HKLM:\Software\Microsoft\DFS\Roots\Domain
Shows all 2008 mode  domain namespaces on the current computer, using the registry: Dir HKLM:\Software\Microsoft\DFS\Roots\DomainV2
Shows all standalone namespaces on the current computer, using the registry: Dir HKLM:\Software\Microsoft\DFS\Roots\Standalone
Shows all namespaces of all types on the current computer, using the registry: Dir HKLM:\Software\Microsoft\DFS\Roots –Recurse | Select PSChildName, ValueCount, Property
Shows properties of the DFS-N service in the registry: Dir HKLM:\System\CurrentControlSet\Services\Dfs
Get status of DFS Service (formatted as list) Get-Service DFS | fl
Starts the DFS-N service (two ways): Get-Service DFS | Start-Service
Get-Service DFS | % { $_.Start }
Shows all WMI objects with DFS on the name (will include some DFS-R ones as well): Get-WmiObject -List *DFS*
Shows DFS Targets on the current computer, using WMI: Get-WmiObject Win32_DFSTarget
Shows selected properties of DFS nodes on the current computer, including it's a root and its state, using WMI: Get-WmiObject Win32_DFSNode | Select Name, Root, State | Format-Table –autosize

I hope that has helped you see how interesting PowerShell can be. Here are a few links for additional information and tutorials: