microsoft powershell tom roeder cs215 2006fa. motivation.net as a platform shell web server database...
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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
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 <ProgID>
eg. Outlook.Application
PowerShell: surprises
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?
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