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COMP075 OS2

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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COMP075 OS2

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  1. Windows Power Shell COMP075 OS2

  2. 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

  3. .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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. Compatibility Names

  21. 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

  22. 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

  23. 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

  24. 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 to generate output

  25. 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

  26. 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

  27. 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)

  28. 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

  29. if if ( condition ) { statement list } elseif … else … • man about_if

  30. Conditions 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 true

  31. Case Statement switch (expression) { value {statement list} … default {statement list} }

  32. 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

  33. 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

  34. 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

  35. 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

  36. 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

  37. 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)

  38. References • Users Guide • http://technet.microsoft.com/en-us/library/cc196356.aspx • Tips • http://technet.microsoft.com/en-us/library/ff730939.aspx

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