microsoft powershell tom roeder cs215 2006fa. motivation.net as a platform shell web server database...

Microsoft PowerShell

Tom Roeder

CS215 2006fa

Motivation

.NET as a platform shell web server database access

Native access to resources eaiser to manage than P/Invoke scripting .NET natively can use reflection idea of managed code throughout

PowerShell: introduction

No more text: traditional style of shell scripting: the pipe

find . –name ‘*.sh’ | xargs zip -@ shfiles what does this command do? many tools for this job

sed, xargs, cut

Instead, pass objects as return values. Why? convert to text as needed richer format

PowerShell: Cmdlets

“built-in” commands for PowerShell “verb-noun” names

eg. get-childitem (= ls) but: new-alias, new-object

single parser for parameters passed as calls to cmdlets

extensible set: can write own cmdlets Aliases

built in with (mostly) standard scripting names

PowerShell: variable syntax

Basic syntax similar to all scripting languages $a = “value” $a = 1 + 2 $a += 137

Built-in support for types $a = [xml]“<test><a>avalue</a></test>” [int]$a = 42 or cast to arbitrary .NET object

PowerShell: parsing

Two contexts: command context

starts with regular character tries to execute command

expression context starts with num, var, or quoted string executes as expression

Can reset mode with “( )” (Get-Date).day + 2

PowerShell: array and hash

$a = 1,2,3,4 $a += 5..10

+ adds elements to array .. is range operator. What is $a[1..3]?

$a[1], $a[2], $a[3]

$a = @{ one=1; val = get-childitem } $a[‘val’] $a.one

PowerShell: if/switch

if { <test> } { <true> } else { <false> } elseif { <test> } { <else> }

switch (<var>) { <val> { <case>; break } … } default case

switch –regex (<var>) { word.* { <case> } … } dropping break gives multiple matches

$_: variable referring to current <var> where { <test> }

PowerShell: looping

while($a –lt 137) { <block> } foreach($var in get-process) { <block> }

IEnumerable support Shorten foreach to %

ls | %{ $_.Length } receive piped objects $_ as before

for { $i = 0; $i –lt 10; $i += 2} { $i } regular for loop

PowerShell: useful operators

&, . call operator $a = “Get-childitem”; &$a # calls get-childitem . used for executing scripts in current context

-as, -is is/as in C# $a –as [int] if { $a –is [System.DateTime] } { … }

PowerShell: functions

function [(args)] { <body> } if Param is first statement, then gives parameters arguments passed in $args input passed in $input

parameter passing on cmd line add –x 2 –y 3 add 2 3

Useful commands

get-member return the members of an object eg. get-member –MemberType property

or, method

Authenticode signing can use certificates to verify scripts checks the hash and returns

PowerShell: errors

throw throw “error” same as ThrowTerminatingError in Cmdlets

trap catch exceptions trap [DivideByZeroException] { <do something> } break/continue semantics

PowerShell: surprises

Drives C, D Env, Alias, HKLM, variable, function mount lets you create others

variable scoping private, local, script, global


import/export –CSV get-unique

$(foreach ($line in get-content C:\Test1\File1.txt) {$line.tolower().split(" ")}) | sort | get-unique

get-item group $x = new-object –COM <ProgID>

eg. Outlook.Application


calc $calc = get-process calc $calc.add_exited({write-host

$this.Processname has exited}) $calc.HasExited $calc.kill() $calc.HasExited

Scriptblocks

a chunk of script a type in PowerShell

$x = [scriptblock]{$y = 137}&$x;

Can be used as an EventHandler delegate this is what’s happening in the last example object parameter -> $this EventArgs parameter -> $_

Cmdlet creation

Subclass of System.Management. Automation.Cmdlet must have an attribute

gives “verb” and “noun” components of name overrides at least one of

BeginProcessing, ProcessRecord, EndProcessing

use make-shell command to include it adds dll to set of cmdlets requires some registry manipulation

Cmdlet creation

Cmdlet parameters add [Parameter] attribute

Mandatory=true|false Position=<index> … others for in-pipeline action

Return value: any object native object facilities allow inspection can use arbitrary code

Example in script

function MyWhere {param ( [scriptblock]$expression )begin { $matches = 0 }process {if ( &$expression ) { $_; $matches++ }}end { "Found $matches matches" }}

Execution Policy

AllSigned require a digital signature and prompt user must agree to run script

RemoteSigned only files from internet need to be signed default setting

Unrestricted no signing required

Attacks on AllSigned?

microsoft powershell tom roeder cs215 2006fa. motivation.net as a platform shell web server database...

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