1. Effective Windows PowerShell
Keith Hill
Windows PowerShell MVP

2. Goals
Provide you with tools & knowledge to make you effective using PowerShell
Teach someone to fish and they can feed themselves
We’ll focus on broad understanding & using commands
Along the way
Provide a mental model of how PowerShell works
Discuss where transfer of learning helps (and hinders)
Point out some gotchas
Show where to get help from the community

3. PowerShell Mental Model
PowerShell is an automation engine for Windows
PowerShell.exe / PowerShell_ISE.exe are just host apps
Engine can be hosted in other applications
PowerShell is a shell and a scripting language
Commands
Providers
Type system
Programming constructs

4. PowerShell Architecture
Host process: PowerShell.exe, PowerShell_ISE.exe, etc
Process Env Block – includes environment variables
Implementation of PSHost* interfaces – used by engine for UI I/O
PowerShell Engine (SMA.dll) – Parses and executes script
Built-in commands
Runspace(s)
Pipeline executes script
Variables
Functions Aliases Module import table

5. Simple C# PowerShell Host App
using System; using System.Collections.ObjectModel; using System.Management.Automation; namespace PowerShellHosting { class Program { static void Main() { using (var ps = PowerShell.Create()) { while (true) { Console.WriteLine("Enter an expression:"); string input = Console.ReadLine(); if (String.IsNullOrWhiteSpace(input)) break; ps.AddScript(input); Collection<PSObject> results = ps.Invoke(); foreach (var result in results) { Console.WriteLine(result); } } } } } }

6. Mental Model – Commands
PowerShell provides “monadic” commands that can be composed in pipeline to accomplish complex tasks
Production-oriented: verify destructive ops before executing
PowerShell commands output objects NOT text
PowerShell commands run “in-process” (not exes)
PowerShell provides:
A common param parsing engine – set of common parameters
An extensible formatting & output engine
Commands are named <verb>-<noun> for consistency
Commands can be verbose for readability Get-Process | Where-Object {$_.PagedMemorySize –gt 100MB} | Foreach-Object {$_.Name}
Or pithy for your wrists (and ego) gps | ? PM –gt 100MB | % Name

7. Mental Model – Providers
Windows has various data stores:
File system, registry, certificate store, environment vars
A Provider is an abstraction over a data store
Instances of providers look like file system drives
C:\, D:\, HKLM:\, Cert:\
Standard set of commands to manipulate
Set-Location (cd), Get-ChildItem, Get/Set-Item, Move-Item, Rename-Item, Copy-Item, Remove-Item
PowerShell exposes some of its own “data stores” via providers: alias, variable, function

8. Mental Model – Type System
ETS – extended type system
Augments objects with new properties & methods necessary to provide better admin experience
.NET types were not designed with admins in mind
FileInfo gets BaseName, VersionInfo
Process gets Company, Cpu, FileVersion, ProductVersion
Other object representations are adapted into PowerShell
WMI, COM, ADSI, ADO
Promiscuously typed language
Tries hard to turn what you have into what you need

9. Type System Demo
TypeSystemDemo.ps1

10. Mental Model – Scripting Language
Provides very useful, C# like programming constructs:
if/elseif/else, for, foreach, while, do while, switch
Provides many useful operators:
-eq/ne/gt/lt/ge/le (why not ==, !=, >, <, >=, <= ?)
-match, -notmatch, -contains, -notcontains, -replace, -split, -join, -and, -or, -not
Users can create their own commands – functions
Users can create their own types – [pscustomobject]
Users can easily create scripts by copying commands they execute in the console into a .ps1 file
Remember, PowerShell does all the hard parameter parsing work for our function.

11. #1 PowerShell Runs Exes
Start simple, use PowerShell instead of CMD to run your favorite utilities: PS C:\> ipconfig /all PS C:\> netsh dump PS C:\> vaultcmd /listcreds:"Web Credentials" /all
Up/down arrows and F7 still work – recalls history
PowerShell tab completes path just as CMD does
PowerShell tab completion is way more extensive
PowerShell follows UNIX rule – you have to use .\foo.exe to run from current directory

12. #2 Four Commands of Discovery
How do you get past the “blank screen of death”?
#1 Get-Command: discover available commands
#2 Get-Help: learn how to use commands
#3 Get-Member: discover what objects can do
#4 Get-PSDrive: discover available data stores

13. Four Commands Demo GetCommandDemo.ps1 GetHelpDemo.ps1
GetMemberDemo.ps1
GetPSDriveDemo.ps1

14. #3 How the Pipeline Works
Piping in other shells pipes text (sometimes binary): $ ps axu | grep python | cut -d' ' -f2
PowerShell pipes pass .NET objects
Each line executed at the console executes in a pipeline
Pipe operator "|" is not what makes it a pipeline
Entire scripts are executed in a pipeline
Objects pass from one stage of pipeline to another: PS C:\> Get-Process python | Foreach-Object {$_.Id}
The automatic variable $_ represents the current pipeline object

15. End of the (Pipe)line
You can specify output formatter and destination: PS C:\> Get-Process | Format-Table | Out-Host
Or let PowerShell choose for you: PS C:\> Get-Process
In this case PowerShell implicitly pipes to Out-Default which selects a default formatter and uses Out-Host
Default formatter selected based on first object
If subsequent objects don’t match format they are displayed using Format-List

16. PowerShell Pipeline in Action
Get-Process | Where {$_.PM –gt 60MB} | Sort ProcessName
System.Diagnostics.Process
Where Process.PagedMemorySize > 60*1024*1024 No
Yes
Sort on Process.ProcessName
Get-Process
out-default
Handles NPM …
Console.Write

17. Pipeline Object Types Can Change
You may know what type the initial command outputs but the next command may output a different type
This works: PS C:\> Get-ChildItem *.ps1 | Where {$_.LastWriteTime -gt (Get-Date).AddMonths(-1)}
But this doesn’t: PS C:\> Get-ChildItem *.ps1 | Select-String psdrive | Where {$_.LastWriteTime -gt (Get-Date).AddMonths(-1)}
Use Get-Member at various pipeline stages to examine the output object type

18. Pipeline Demo
PipelineDemo.ps1

19. #4 Formatting & Output Formatting – rendering object to formatted text
Determine what parts of the object are to be displayed
Determine what display format to use:
Table, list, wide and custom
User can explicitly choose: Format-Table/List/Wide/Custom
Output – sending formatted text to desired location
Out-File, Out-String, Out-Printer, Out-Host (default)
Output sent to Host goes through HOST UI interface: PSHostUserInterface.WriteLine (String)

20. How Objects Get Rendered as Text
Formatting directions
Format (ps1xml) files provide directions on what properties to display and what format to use
Reflection over public properties
Public properties are display
Number of properties determines the formatter used
<= 4 displays data in a table
> 5 displays data in a list
Object.ToString() – last ditch if no public properties

21. Formatting Demo
FormattingDemo.ps1

22. Format & Type Data Files
Format data file instructs PowerShell how to display a particular object type in various formats
Type data file instructs PowerShell what properties to display and specifies new properties: AliasProperty, NoteProperty, ScriptProperty
Examine
Format data file: $pshome\DotNetTypes.format.ps1xml
Type data file: $pshome\types.ps1xml

23. #5 Understanding Parsing Modes
PowerShell parses for both command execution & expression evaluation
String isn’t the only literal type parsed:
int, double, decimal, bool, array, hashtable
Command execution: must feel natural e.g.: PS C:\> Select-String xyzzy c:\foo.txt PS C:\> notepad.exe c:\foo.txt
Expression evaluation: scripting must feel natural e.g.: PS C:\> $sum = 6*7 PS C:\> if ($sum –eq 42) {"What's the question"} PS C:\> 'Select-String xyzzy c:\foo.txt' >> foo.log PS C:\> [Math]::Max($sum, 100) PS C:\> [int]::Parse('2A8D', 'HexNumber') # quote strings

24. The Two Parsing Modes Argument (command) parsing mode
Strings don’t need to quoted
Numbers are parsed as strings
Certain characters kick parsing into expression mode:
' " and (
Expression parsing mode
Strings must be quoted
Numbers not in quotes are treated a numerical values
Certain characters kick into argument parsing mode
\/ - path characters e.g. $pwd\foo.txt – no quoting necessary
= - the value on the right can be either a command or expression
Within expression, start new parsing context with ( or $(

25. Parsing Mode Determination
By initial characters of line and after: (, $( , { and =
Parsing mode
Patterns
Argument/Command
[_aA-zZ] # command name
& # call operator .\s # dot source operator [./\] # start of a path .[^0-9./\ ] # .n7.exe ok, .7 & .7kb are nums [0-9]+[_aA-zZ] # except for d, kb, mb, gb, tb
Expression
[0-9]*\.?[0-9]+(d|kb|mb|gb|tb|pb)? ' " $ # variable reference or subexpression # hashtable and splatting (

26. PowerShell Parsing Gotcha
Interop with executables taking complex arguments can be very problematic in PowerShell
Quotes get lost
PowerShell interprets certain chars: ( { ; `
Stop parser symbol kicks into dumb parsing mode: icacls --% X:\VMS /grant Dom\HVAdmin:(CI)(OI)F
Can use env variables: $env:table = 'AdventureWorks.Person.Contact' sqlcmd -S .\SQLEXPRESS -v lname="Gates" --% -Q "SELECT FirstName,LastName FROM %table% WHERE LastName = '$(lname)'"

27. Parsing Modes Demo
ParsingModedDemo.ps1

28. #6 Error Handling Two flavors
Non-terminating
Terminating
Non-terminating errors don’t alter control flow
Can be converted to terminating errors with:
ErrorAction common parameter
$ErrorActionPreference variable
Terminating errors alter control flow
Use try/catch to handle terminating errors
Or let the script error out on a terminating error

29. Error Related Variables
$Error - PowerShell stores all errors in this collection
$Error[0] always contains the most recent error
$MaximumErrorCount – max size of $Error collection
$? – boolean execution status of last command
True indicates command succeeded without any errors
False indicates complete or partial failure
True for exes returning 0 and False any other exit code
$LastExitCode – int containing last exe’s exit code

30. Error Handling Demo
ErrorHandlingDemo.ps1

31. Popular Modules / Tools / Repos
PowerShell Community Extensions & PSGet Gallery
PSReadline & PSGet Gallery
PowerShell Tools for Visual Studio
ISESteriods 2.0
PoshCode.org

32. Help Resources StackOverflow http://stackoverflow.com/tags/powershell
PowerShell.org
MS TechNet ScriptCenter forums
Effective Windows PowerShell (free) eBook

33. Make PowerShell Better
Report a bug
Submit a suggestion (enhancement request)
Vote on already submitted bugs & suggestions

34. Questions?