Lecture 13, 14 & 15 c# cmd let programming and scripting

Lectures 15 - 17:
C#, cmdLet
programming &
scripting
Network design & Administration

Why does a Systems Administrator
need to know about programming?
• Tools not available to perform task
• Have to write new tools
• Use scripting to provide more power than

Network Design & Administration
executing single command line tools
• Automate tasks
• Need to alter the OS (if Unix based)
• There are lots of reasons why a knowledge
of programming is essential! 2

Powershell
• Powershell is “the next generation command shell and
scripting language”[1]
• Provides access to lots of powershell programs (cmdlets)
• Cmdlets can be joined together (output -> input)

• Powershell provides a set of scripting commands to
facilitate in linking cmdlets together (more later)
• Can program your own cmdlets to do specific tasks

3

What do you need to know to
be able to program a cmdlet?
• C# !
• C# is a C++/Java like language
• C# requires the .Net framework to be installed
• Cmdlets are written in C# but you need to:
• Extend the PSCmdLet class

• Provide parameter attributes
• Implement the following methods:
• BeginProcessing
• ProcessRecord
• EndProcessing
• Provide your code!
• Before we look at cmdlet programming in more detail, a quick 4
introduction to C# is in order!
[4]

C# Data types
• C# has the same primitive data types that you find in C++ and
Java
• int e.g. int value = 5;
• bool e.g. bool receivedInput = false;
• float e.g. float value = 8.5;

• arrays e.g. string []params; BUT!

• More complex data types:
• String
• List
• ArrayList
• Stack
• Queue 5
• …

C# Classes
• In C#, everything is an Object
• A class provides the blueprint as to what data and operations
it can offer
• However, you have to use the class blueprint to create an

object instance before you can access it
• Follows a similar syntax to a Java Class.

public class MyFirstClass{
public MyFirstClass() {
// Constructor …
} Use dot notation tonew keyword
Use the
access the objects
to instantiate object
}
methods 6
MyFirstClass m = new MyFirstClass();
m.print();

Anatomy of a C# Program
using System;
1. Using (import other
namespace ConsoleApplication1
classes)
{ 2. Namespace
class MyFirstProgram 3. Class definition
{
private String _message = "Hello ";
4. Private data
5. Class constructor

public MyFirstProgram(String userName) 6. One Main method
{
per program (has to
Console.WriteLine(_message + userName);
}
be static)
7. Parameter passing
public static void Main(String[] args) 8. Instantiating a new
{
object
MyFirstProgram myProg = new MyFirstProgram("Clark");
} 9. Writing output to
} the console
} 7

C# Strings
• Strings are objects of the System.String Class
• Can assign a sequence of characters to them…
String machineName = "CIB108-34";
• i.e. use the assignment operator =

• You can join strings together…
String fullName = machineName + ".ads.ntu.ac.uk";
• Using the + operator
• Because String is a class there are several handy methods and
properties it provides…
• Length – returns the number of characters in the string
• Substring( int startPosition, int length) – returns characters
between start and start+length characters 8

Inheritance
• C# allows you to inherit functionality from another class.
public class Employee
{
private String name = string.Empty;
public Employee(String n)

{
public class Manager : Employee
name = n; Inherits the print() method
{}
private List<Employee> employeeList = new List<Employee>();
public void print()
{ public Manager(String name) : base(name)
Console.WriteLine("Employee name: " + name );
{
}
}
}
public void manages(Employee employee)
{
employeeList.Add(employee); 9
}
}

The Object Class
• When you create a new class (for example):

using System;

public class MyFirstClass

{
public MyFirstClass()
{
// …
}
}

• You can define a class and not provide any explicit inheritance.
• However, all classes derive from a base class even if it is not 10
explicitly stated.
• This is the object class.

The object class
• Because all classes derive from object within C# we can use the
object class as a way of providing a generic interface to methods
public void add(object obj) { }

• This is done by boxing and unboxing which also allows value types
(primitive data types) to act like reference types (objects)

• For example, boxing value types:
int myValue = 1000;
object obj = myValue;
int newValue = (int)obj;
obj
myValue
int newValue
1000
1000 1000
11
• However, unboxing must be explicit!

Namespaces
• C# provides you with hundreds of classes that you can use within
your programs.
• Each class you create/use will have a name (e.g.):
public class ListCommand

• What happens if there is another class called ListCommand?

• You can use a Namespace to limit the scope of any classes that you
define: namespace myLibrary
{
public class ListCommand
{
// ...
}
}

• Now ListCommand is visible within the myLibrary namespace 12
• You can now access your class as:
myLibrary.ListCommand ...

Interfaces
• An interface allows you to define a specific interface to a class.
• Any class that implements that interface will have to provide a
set of pre-defined method signatures.
namespace myLibrary

{
interface MyListInterface
{
void add(object onj);
object get(int index);
int size();
void toString();
}
} 13

Interfaces
• To use an interface you have to specify a class which inherits
the interface
namespace myLibrary
{
interface MyListInterface

{
void add(object onj);
object get(int index);
int size();
void toString();
}

public class MyList : MyListInterface
{
public MyList() { } 14
}
}

this and is keywords
• this
• Refers to current instance of an object
• Example:
private string name;
public void setName(string name) {

this.name = name;
}

• is
• provides you with a way to determine if the object supports an
interface
• If it does, then you can access methods within it
• Syntax:
<expression> is <type>
• Example: 15
Employee CKent = new Employee("Clark Kent");
if( CKent is Employee ) CKent.print();

C# Control Structures
• C# provides the same control structures as C/C++ and Java
• if statement
if( x == 10 ) {
// …
} else {
// ..

}

• Remember - when comparing objects
if( obj1 == obj2 ) {}

• Isn’t comparing that the two objects contain the same data but is
instead comparing the pointers of each object.
• But Strings are different!
String name1 = "clark";
String name2 = "lois";
16
if( name1 == name2 ) Console.WriteLine("they are the same!");
else Console.WriteLine("they are not the same!");

C# Control Structures
• C# provides the same control structures as C/C++ and Java

• Switch statement
switch( value ) {

case 1:
Console.WriteLine("Option 1!");
break;
case 2:
break;
default:
break; 17
}

Loops
• For loops are the same as in C++/Java
for (int iCounter = 0; iCounter < 10; iCounter++)
{
Console.WriteLine("counter = " + iCounter);
}

• Foreach:
List<string> myList = new List<string>();
for (int counter = 0; counter < 10; counter++) {
myList.Add("item " + counter);
}
foreach (string value in myList) {
Console.WriteLine(value);
18
}

Reading and Writing to the
console
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)

{
Console.WriteLine("Enter first number:");
int value1 = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Enter second number:");
int value2 = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("multiplying {0} by {1} gives {2}",
value1, value2, (value1 * value2));
}
19
}
}

Exception handling
• C# provides you with throw and try-catch statements so that
you can handle any unwanted exceptions
• Program {
class Classes that you use within your C# code will usually throw an
rd
public List<string> myList =(especially if you are relying on 3
exception if an error occurs new List<string>();
static api’s / Main(string[] args) {
part void libraries)

Program m = new Program();
m.myList.Add("item " + counter);
}
Console.WriteLine(m.getIndex(50));
}
public string getIndex(int index){
if (index > myList.Count) throw new IndexOutOfRangeException();
else return myList[index]; 20
}
}

Exception handling
class Program {
public List<string> myList = new List<string>();
static void Main(string[] args) {
Program m = new Program();
m.myList.Add("item " + counter);

}
Try {
Console.WriteLine(m.getIndex(50));
} catch (IndexOutOfRangeException error) {
Console.WriteLine("Error occurred: " + error.Message);
}
}
public string getIndex(int index) {
if (index > myList.Count) throw new IndexOutOfRangeException();
else return myList[index]; 21
}
}

Properties
• In C# you can use properties to access private data
• Use the get and set methods to allow read or write access
Private data stored
within the class

The get method
returns the value of private string _name;
the private data The property!
element. Used when
access the property by public string Name
name or on RHS of =
{
Special keyword in C#.
get { return _name; } Gives the value from
set { _name = value; } the RHS of an =
The set method allows operation.
you to assign a value }
to the private data 22
element. This is called Examples:
automatically when = Name = “Clark”;
is used String userName = Name;

Exercise!
• Spend 5 minutes to work out what
errors are in the code in the hand-out.
• The person who identifies the correct

number of errors gets a prize!

23

Now back to cmdlets … Cmdlet naming[2]
• Cmdlets are named using a verb-noun pair
• Verbs are used to describe what action the cmdlet will perform
• Nouns are used to describe what entity the cmdlet will perform the
action on
• Examples (encountered in the labs):

• New-ADComputer
• Get-Help
• Set-ADUser
• There are lots of pre-defined verbs (stored in classes):
• VerbsCommon VerbsLifeCycle
• VerbsCommunications VerbsSecurity
• VerbsData VerbsOther
24
• VerbsDiagnostic

Sending input to cmdlets
• Cmdlets can accept parameters
new-gpo –name “Publishers Policy”

• Cmdlets can also be chained together so that the output of
one can be the input to another.

• For example:
new-gpo –name “Publishers Policy” | new-gplink –target
“ou=publishers, dc=testnetwork, dc=com”

• Here, new-gpo is creating a new GPO object and passing it
(using the pipe symbol |) to the new-gplink cmdlet.

25

Anatomy of a cmdlet
using System;
using System.Collections.Generic;
using System.Text;
using System.Management.Automation;
namespace HelloWorldExample {
[Cmdlet(VerbsCommunications.Send, "Hello World Example!")]

public class HellowWorld : PSCmdlet {
[Parameter(Mandatory = true)]
public string yourName {
get { return userName; }
set { userName = value; }
}
private string userName;
protected override void ProcessRecord() {
WriteObject("Hello" + userName + "!"); 26
}
}
}

Processing within cmdlets
• The Cmdlet and PSCmdlet classes provide the following methods:
• BeginProcessing
• ProcessRecord
• EndProcessing
• These methods need to be implemented by the developer

• Sending objects through a pipeline between cmdlets can be
demonstrated by the following :-

Input Pipeline Output Pipeline

Object 1
cmdlet
Object 2
Begin Process End
Object 3 Processing Record Processing 27
New Output
Object 2
Object3

Snap-ins
• Once you have finished writing your C# cmdlet
you have to create another file which contains
snap-in information.
• Snap-ins are used to register cmdlets with

powershell and to setup any registry entries
• If you do not register a cmdlet within powershell
you will not be able to run it
• A snap-in for the cmdlet would be added to your
project and get linked in when the project is
28
compiled

Anatomy of a Snap-in
using System;
using System.Collections.Generic;
using System.Text;
using System.Management.Automation;
using System.ComponentModel;
namespace ListCommand {
[RunInstaller(true)]

public class ListCommandSnapIn : PSSnapIn {
public override string Name {
get { return "ListCommand"; }
}
public override string Vendor {
get { return "Jon Robinson"; }
}
public override string Description {
get { return "New directory listing command"; }
29
}
}
}

Compiling cmdlets and linking
into Powershell
1. Cmdlets can be created and compiled within visual
studio
• Need a special template project to create cmdlets
which can be downloaded from the web[3]
2. Can also be compiled using the .Net framework C#

compiler (csc.exe)
• Found under windowssystem32Microsoft.Net<.net
version>
3. Use the installutil command to register the cmdlet in
powershell
4. Use add-pssnapin <new cmdlet> to access cmdlet from
powershell prompt 30

Powershell Scripting
• Powershell provides a rich scripting language
• Used to provide more complex functionality
linking cmdlet’s together
• Types of language features available:

• variables
• if/else statements
• switch statements
• for loops
• command line parameter passing 31

• Etc…

Powershell scripting example [1]
[int]$intPing=10
[string]$intNetwork="127.0.0."
Variables have the following syntax:
[<data type>] $<variable name> = <data value>
for($i=1; $i -le $intPing; $i++) {
Available data types:
$strQuery = "select * from win32_pingstatus

[array] [bool]
where address = '" [char]
[byte] + $intNetwork + $i + "'"
$wmi [decimal]
= get-wmiobject -query $strQuery
[double]
[hashtable] [int]
"Pinging $intNetwork$i ..."
[long] [string]
if( $wmi.statuscode -eq 0 )
[single] [xml]
{"success"} -eq (equal to)
else If statement syntax: -lt (less than)
{"error: " + $wmi.statuscode + " occurred"}
-gt (greater than)
if( $<variable name> <evaluation expression> <value> )equal to)
-ge (greater than or 32
} {"success"} -le (less than or equal to)
else -ne (not equal)
{"fail"}

Powershell switch example
Switch statement syntax:
switch <expression evaluation type> ($<variable name>) {
… expressions …
}

[int] $simpleSwitchExample = 2

switch($simpleSwitchExample) {
1 { "Option 1" }
2 { "Option 2" }
3 { "Option 3" }
default { "No idea..." } 33
}

Powershell switch example
[string] $regularExpressionSwitchExample = "1234"
[int] $size = 0

switch -regex ($regularExpressionSwitchExample) {
"d{4}" { $size = 4; break; }
"d{3}" { $size = (regular expression)
-regex 3; break; }
-wildcard (wildcard!)

"d{2}" { $size = 2; break; }
"d{1}" { $size = 1; break; }
default {
"No idea..."
$size = -1
}
}

if( $size -gt 0 ) { "The string had " + $size + " characters" }
else { "Wasn't able to work out how many characters!" } 34

Getting input from the user
• Scripts can interact with the user to provide more
functionality.
• Scripts can display information by just saying “message…”.
• However, this is not formatted.
• Can use the Write-Host cmdlet to display output.

• Can format the message (colours, spaces, etc)
• For example:
Write-host “hello world” –foregroundcolor black –backgroundcolor white
• Scripts can get input from the user by using the Read-Host
cmdlet.
• For example:
$ipAddress = Read-Host “Enter the ip address:”
• Can use the –AsSecureString option to mask what has been 35
entered.
$password = read-host –assecurestring “Enter your password:”

Powershell functions
function display {
param ([string]$message="")
Write-Host "Your message is $message"
}

display "hello world"
Un-typed – could be any
type of information
function display( $message ) {
Write-Host "Your message is $message"
}

display "hello world" 36

Powershell functions
function display {
param ([string]$message="")
param ([int]$repeat=1)
$returnMessage = “”
for($count=1; $count –le $repeat; $count++) {

Write-Host "Your message is $message“
$returnMessage = $returnMessage +
“Your message is $message”
}
return $returnMessage
}
37
display("hello world“, 5)

Next Time & References
• Updating Systems

References
[1] “Windows PowerShell Scripting Guide”, Wilson, E., Microsoft Press
[2] http://msdn.microsoft.com/en-us/library/windows/desktop/ms714428%28v=vs.85%29.aspx

[3] http://channel9.msdn.com/forums/sandbox/249904-Windows-PowerShell-Visual-Studio-2005-
Templates-C-and-VBNET
[4] http://msdn.microsoft.com/en-us/library/zw4w595w.aspx

38

Lecture 13, 14 & 15 c# cmd let programming and scripting

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