1. Microsoft PowerShell Tom Roeder CS215 2006fa

2. 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

3. 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

4. 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

5. PowerShell: variable syntax Basic syntax similar to all scripting languages $a = “value” $a = 1 + 2 $a += 137 Built-in support for types $a = [xml]“ avalue ” [int]$a = 42 or cast to arbitrary.NET object

6. 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

7. 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

8. PowerShell: if/switch if { } { } else { } elseif { } { } switch ( ) { { ; break } … } default case switch –regex ( ) { word.* { } … } dropping break gives multiple matches $_: variable referring to current where { }

9. PowerShell: looping while($a –lt 137) { } foreach($var in get-process) { } IEnumerable support Shorten foreach to % ls | %{ $_.Length } receive piped objects $_ as before for { $i = 0; $i –lt 10; $i += 2} { $i } regular for loop

10. 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] } { … }

11. PowerShell: functions function [(args)] { } 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

12. 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

13. PowerShell: errors throw throw “error” same as ThrowTerminatingError in Cmdlets trap catch exceptions trap [DivideByZeroException] { } break/continue semantics

14. PowerShell: surprises Drives C, D Env, Alias, HKLM, variable, function mount lets you create others variable scoping private, local, script, global

15. PowerShell: surprises 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 eg. Outlook.Application

16. PowerShell: surprises calc $calc = get-process calc $calc.add_exited({write-host $this.Processname has exited}) $calc.HasExited $calc.kill() $calc.HasExited

17. 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 -> $_

18. 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

19. Cmdlet creation Cmdlet parameters add [Parameter] attribute Mandatory=true|false Position= … others for in-pipeline action Return value: any object native object facilities allow inspection can use arbitrary code

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

21. 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?