COMP075 OS2

Windows Power Shell

What is it

• A command line OS shell

• Replaces DOS

– CLI and .bat

• Also replaces Windows Script Host

– A bad idea from the start

• And netsh, and WMIC

• Built on .net

– Provides access to COM objects

.net?

• A framework that, among other things provides access to COM objects

• It was intended to replace the COM interface by providing .net wrappers for the com objects

– Nevertheless, components like the office ribbon control are implemented using COM directly

• .net was intended to ease development by hiding implementation details

COM

• Component Object Model

• Introduced in 1993

• A language agnostic interface standard

– As opposed to, say, the C calling convention

• Basis for OLE, ActiveX, COM+ DCOM

• Used for IPC

• Supplanted DDE

DDE• Dynamic Data Exchange

• An IPC protocol that allowed text based “conversations” between processes

• The original basis for OLE

– Object Linking and Embedding

– Let you put spreadsheets in a word document

• Text conversations considered not flexible enough, so COM was introduced as the basis for OLE2 (later renamed OLE)

• COM designed for any software components

– Not just OLE

What was wrong with text, or simple binary interface?

• Too inflexible

• Format had to remain the same to be understood by the reading process

• Microsoft is really bad at leaving things alone

• Object interfaces avoid this problem

• Data extracted from interface by name

– So only the name has to be stable

• Objects know the format of the data and can inform the recipient

• Perfect for heterogeneous development environment where no one talks to each other

ActiveX

• Just before COM, MS introduced VBX

– Visual Basic Extensions

– C or C++ user interface subroutines meant to be called from Visual Basic main program

• These became OLE controls (OCXs) based on COM

• Later renamed ActiveX Controls for use in browsers

– Called controls since originally meant for user interface

– Actually general purpose programs

• Now all OLE is known as ActiveX except in MS Office

COM and the registry

• COM objects belong to classes

• They have interfaces and type definitions

• Stored in the registry

– HKEY_CLASSES_ROOT\CLSID for classes and HKEY_CLASSES_ROOT\Interface

• Registration-free COM stores these data in an XML manifest

• Registry use can introduce DLL hell since only one version can be registered

More .net

• Consists of FCL (Framework Class Library)

– User interface, data access, db connectivity, crypto, development, networking, graphic rendering XML manipulation

• And CLR (Common Language Runtime)

– An application VM providing security, memory management, exception handling etc

• Visual Studio is an IDE for .net programs

Some .net features

• Wrappers to provide access to COM objects

• Common Type System and Common Language Infrastructure specifications provide for language independence

• CLI implemented through CLR

• CLI program compiled to CIL (Common Intermediate Language) and stored in assemblies

Assemblies

• Code is in PE format

• Assemblies can comprise many files

• One is a manifest containing metadata

• Name is simple name + version + culture + public key token

• Considered the same if equal in all but revision

– Version = major + minor + build + revision

– This is meant to avoid DLL hell

• Can be process (exe) or library (dll) assembly

Public Key

• A Strongly Named assembly can be stored in the Global Assembly Cache

• Must have some components signed with private key corresponding to public key in the assembly name

• All versions of assembly must be signed by same key

• All assemblies depended on must be strongly named

• Global Assembly Cache can contain two versions of the same assembly, but file system can't

Power Shell and .net

• Most PS functions provided through commands

– But in PS are called cmdlets

• cmdlets are .net classes (programs)

• Can be combined into scripts or run in Win32 console

• Runtime can be embedded in other applications so that a cmdlet can access interfaces usually only available through a gui

• cmdlets can access COM objects and WMI through .net and file systems and registry through PS providers

Types of commands

• cmdlets

– Specially designed .net classes

– Run as part of the PS process

• PS scripts (.ps1)

• PS functions

– Subroutines, like in bash

• Standalone programs

– Run as separate process

cmdlets

• Names follow verb-noun pattern which makes them annoyingly large

– Get-Help

– But abbreviations are provided as aliases

• Input and output are .net objects, or collections of objects

– Not text

– Except command line parameter input

• Last stage in pipeline automatically sent to Out-Default cmdlet to convert object to text

cmdlet structure

• Class def may implement BeginProcessing, ProcessRecord and EndProcessing methods

• ProcessRecord required to process pipeline input

– Invoked once for each object in a collection

• Must have .net attribute “CmdletAttribute” containing cmdlet name

• ValueFromPipeline attribute distinguishes ParameterAttribute properties that originate in pipeline

pipelines

• | operator joins one cmdlet to another in a pipeline

• Like DOS or bash pipelines but .net objects rather than text

– Parsing or serializing not required

– Format doesn't matter, needn't remain stable

• Objects can use standard ToString() method to format attributes as text, or include custom formatters

Providers• Cmdlet can reference any .net API including

data access APIs

• Or use included PS providers

• Providers available for

– File system

– Registry

– Certificate store

– Namespace for aliases, variables and functions

– All looks like a file system (like linux but with drive letters)

• Some cmdlets access WMI

Command Names

• Verb-Noun format

• Restricted set of verbs

– Get New Restart Resume Set Start Stop Suspend

• Nouns used consistently across commands

• Two letter abbreviation aliases

– Remove-Item ri

– Copy-Item ci

– Move-Item mi

– Rename-Item rni

– Get-Content gc

Compatibility Names

Object Pipelines

• Like pipelines in DOS and bash, but data passed to next command in the form of an object

• Unlike text, data in an object have names and other attributes so next stage in pipeline can be aware of these metadata for formatting and other purposes

• To display in text form, last stage of pipeline is automatically Out-Host (oh)

• Get-member shows you the components of an input object

Out commands

• Out-Host (oh) converts to text

-paging outputs through pager

“more” is a function that acts as a synonym

• Out-Null Discards the output

• Out-Printer prints

• Out-File -FilePath … sends to a file

• Out- command has to be last in the pipeline

Format Commands

• format-wide

– Like dir /w

– Extracts one property (usually name), displays in two columns

• Format-table

– Table with property name headings

– The default

• Format-List

– Lines with property name, value

– Repeats for each object

Directories

• Get-Location (pwd) shows current directory

– Note: In PS this could be a network or other path including a registry path or the process environment

• Set-location (cd) changes directory

• cd ..

• “Push-location path” cd's and pushes to stack

• Pop-location pops from stack and cds

-passthru option also sends location to output

Drive Letters

• A more generalized concept

• a: c: etc as usual

• HKCU: HKLM: etc for root of registry trees

• Cert: for certificate store

• Env: for the process environment

• Get-psdrive lists available drives

Help!

• Get-command lists available commands

• Get-command get.* lists get commands

• gcm command1 -syntax gets syntax for command1

• Get-help command-name gets basic help

• Or command-name -?

• help command-name -examples

• man command-name -detailed

• help command-name -full

Scripts

• More like a real programming language

• Variables, literals, functions, control structures

• Variable names start with $

– Can be assigned output of a cmdlet

– Or any other value

• Literals can be single or double quoted like in bash or perl

• $args is the array of parameters

• Can use associative arrays (like perl hash)

Permission to Run Scripts

• ExecutionPolicy by default may forbid execution of scripts, or require that they be signed

• Set-executionpolicy bypass localmachine allows any script to run for anyone

• Like bash, PS doesn't search current directory for scripts

• To run script other than from path specify complete path

• .\menu.ps1 for script in current directory

– Note .ps1 for PS scripts

if

if ( condition )

{

statement list

}

elseif

…

else

…

• man about_if

Conditions

man about_Comparison_operators

• -eq -ne -lt -gt -le -ge

– If left side is a list, returns nothing, or the values for which the comparison is true

– If left is a scalar returns true or false

• string -match/-notmatch regex

• Can test on the command line

2 -eq 2

true

Case Statement

switch (expression)

{

value {statement list}

…

default {statement list}

}

switch Options

switch -regex (value)

{

regex {statement list}

…

• Break

– Switch statement will match multiple possibilities

– To prevent this put break statement at end of each statement list

• Arrays: If value is an array, each element is compared

while

while (condition) {

statement list

}

• break can be used to exit from the entire statement

mylabel: while …

break mylabel

• Label used to specify which loop to break from in case they were nested

Writing to the Screen

clear -- will clear the screen

• As will clear-host

echo $1 –Writes $1 to the screen

• As will

Output-Host -InputObject $1 (oh)

• Or

Write-Host $1

• Or just

$1

Asking the User for a Choice

• Three part process

• First: Create objects that define the choices

• Second: Create a menu object that offers these choices

• Third: Activate a menu with a Title, a message to the user, and the menu object

Define the Choices

• $First = New-Object System.Management.Automation.Host.ChoiceDescription "&First", "First Choice"

• $First contains the object

• First is the short description of the Choice

• &F makes “F” a hotkey for this choice

• "First Choice" appears if help is requested

Create Menu ObjectAsk for Choice

• $options = [System.Management.Automation.Host.ChoiceDescription[]] ($First, $second)

• $title = 'two choice menu'

• $message= “enter a choice”

• $result = $host.ui.PromptForChoice($title, $message, $options, 0)

A Possibly Easier Way

• read-host gets a value from the user and returns the value entered

$choice = read-host– Stores the value in $choice

• If you want, you can craft a menu and get a response this way, but you won't get the built in supports (like help text for the user, error handling) that the previous method provides

References

• Users Guide

– http://technet.microsoft.com/en-us/library/cc196356.aspx

• Tips

– http://technet.microsoft.com/en-us/library/ff730939.aspx