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Windows Power Shell. COMP075 OS2. 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?.

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Windows power shell

Windows Power Shell


What is it
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

Comp075 os2

  • 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

Comp075 os2

  • 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

Comp075 os2

  • 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
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

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

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


  • 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 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
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
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


  • 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
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
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
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


  • 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
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


  • | 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


  • 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
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

Object pipelines
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 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 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


  • 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 to generate output

Drive letters
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

Comp075 os2

  • 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


  • 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
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

Comp075 os2

if ( condition )


statement list




  • man about_if


man about_Comparison_operators

  • -eq -ne

    • Includes an equal (non-equal) value

  • -lt -gt -le -ge

  • string -match/-notmatch regex

  • Can test on the command line

    2 -eq 2


Case statement
Case Statement

switch (expression)


value {statement list}

default {statement list}


Switch options
switch Options

switch -regex (value)


regex {statement list}

  • Break

    • Switch statement will match multiple posibilites

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

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


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
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


Asking the user for a choice
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
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 object ask for choice
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)


  • Users Guide


  • Tips