Mastering windows powershell scripting

Chapter 1. Variables, Arrays, and Hashes

• Variables
• Arrays
• Hashes
• Deciding the best container for your scripts

Variables

$myString = "My String Has Multiple Words"
$myString 

Tip

You are able to reuse variables without deleting the content already inside the variable. The PowerShell interpreter will automatically overwrite the data for you.

$a = "1"
$b = "2" 
$c = $a + $b
$c

$a = 1
$b = 2
$c = $a + $b
$c

Objects are vastly different than strings and numbers. Objects in PowerShell are data structures that contain different attributes such as properties and methods with which one can interact. Object properties are descriptors that typically contain data about that object or other related objects. Object methods are typically sections of code that allow you to interact with that object or other objects on a system. These objects can easily be placed in variables. You can simply place an object in a variable by declaring a variable and placing an object in it. To view all of the object’s attributes, you can simply call the variable containing the object, use a pipe character |, and use the get-member cmdlet.

To place an object in a variable and retrieve its attributes, you need to do this:

$date = get-date
$date
$date | get-member

The output is shown in the following screenshot:

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In this example, you will learn how to place an object into a variable. You first start by declaring the $date variable and setting it equal to the output from the get-date cmdlet. When you execute this, the get-date cmdlet references the System.Date class, and the $date variable inherits all of that object’s attributes. You then call the $date variable and you see that the output is the date and time from when that command was run. In this instance, it is displaying the DateTime ScriptProperty attribute on the screen. To view all of the attributes of the System.Date object in the $date variable, you pipe those results to the get-member cmdlet. You will see all of the attributes of that object displayed on the screen.

If you want to use the properties and method attributes of that object, you can simply call them using dot notation. This is done by calling the variable, followed by a period, and referencing the property or method.

To reference an object’s properties and method attributes, you need to do this:

$date = get-date
$date.Year
$date.addyears("5")

The output of this is shown in the following screenshot:

This example shows you how to reference an object’s properties and method attributes using dot notation. You first start by declaring the $date variable and setting it equal to the output from the get-date cmdlet. When you execute this, the get-date cmdlet references the System.Date class, and the $date variable inherits all of that object’s attributes. You then leverage dot notation to reference the Year property attribute by calling $date.Year. The attribute will return 2015 as the Year property. You then leverage dot notation to use the AddYears() method to increase the years by 5. After entering the $date.addyears("5") command, you will see an output on the screen of the same month, day, and time; however, the year is incremented by 5 years.

Arrays

The following table represents an array with a single dimension:

When you are storing, manipulating, or reading the data in an array, you have to reference the position in the array the data is residing. The numbers populated in the table’s Index number column are representative of the location within the array. You will see that array’s numbering starts at the number 0, and so the first data would be in cell 0. If you call the array at position 0, the result would be the position value of Example 1. When building the array, you will see that each value in the array values is separated by a comma. This tells the PowerShell interpreter to set a new array value.

First, you can start by building the array in the preceding table by entering the following command:

$myArray = "Example 1", "Example 2", "Example 3", "Example 4", "Example 5"
$myArray

The output of this is shown in the following screenshot:

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The preceding example displays how to create an array of strings. You first start by declaring a variable named $myArray. You then place multiple strings of text separated by commas to build the array. After declaring the array, you call the $myArray array to print the values to the console. It will return Example 1, Example 2, Example 3, Example 4, and Example 5.

Retrieving data at a specific position in an array is done through the use of brackets. To retrieve the value of 0 from the array, you would do the following:

$myArray = "Example 1", "Example 2", "Example 3", "Example 4", "Example 5"
$myArray[0]

The output of this is shown in the following screenshot:

Картинка с сайта: www.packtpub.com

The preceding example displays how you can obtain array data at a specific position. You first start by declaring a variable named $myArray. You then place multiple strings of text separated by commas to build the array. After declaring the array, you call $myArray[0] to access the position value of index number 0 from the array. The preceding example returns the value of Example 1 for the index number 0.

Arrays can become more complex as you start adding dimensions. The following table represents a jagged array or an array of arrays:

While accessing data in a jagged array, you will need to read the cell values counting at 0 for both dimensions. When you are accessing the data, you start reading from the index number first and then the position value. For example, the Example 1 data is in the index number of 0 and the position value of 0. This would be referenced as position [0][0]. Subsequently, the data
Blue is in the index number of 4 and position value of 1. This would be referenced as position [4][1].

To do this for yourself, you can build the preceding table by entering the following command:

$myArray = ("Example 1","Red"), ("Example 2","Orange"), ("Example 3", "Yellow"), ("Example 4", "Green"), ("Example 5", "Blue")
$myArray[0][0]
$myArray[4][1]

The output is shown in the following screenshot:

Картинка с сайта: www.packtpub.com

This example displays how to create a jagged array and accessing values in the array. You first start building the jagged array by declaring the first array of "Example 1" "Red", second array of "Example 2" "Orange", third array of "Example 3" "Yellow", fourth array of "Example 4" "Green", and fifth array of "Example 5" "Blue". After building the array, you access the word Example 1 by referencing $myArray[0][0]. You then access the word Blue by referencing $myArray[4][1].

After you create an array, you may need to update the values inside the array itself. The process for updating values in an array is similar to retrieving data from the array. First you need to find the cell location that you want to update, and then you need to set that array location as equal to the new value:

Given the preceding table, if Jane’s last name needed to be updated to display Doe instead of Smith, you would first need to locate that data record. That incorrect last name is located at index number 1 and position value 1, or [1][1]. You will then need to set that data location equal (=) to Doe.

To do this, you need to enter the following command:

$myArray = ("John","Doe"), ("Jane","Smith")
$myArray
$myArray[1][1] = "Doe"
$myArray

The output of this is shown in the following screenshot:

Картинка с сайта: www.packtpub.com

This example displays how you can create an array and update a value in the array. You first start by defining $myArray and use "John","Doe", "Jane", and "Smith" as the array values. After calling the variable to print the array to the screen, you update the value in index number 1, position value 1, or $myArray[1][1]. By setting this position equal to Doe, you change the value from Smith to Doe:

In instances where you want to append additional values to the array, you can call the array variable with the += command and the data you want to add to the array. This looks like $array += "New Array Values". The += command is a more efficient method of performing the commands $array = $array + "New Array Values".

To add data into an array and make the preceding table, you can do the following operation:

# Create the Array
$myArray = ("John","Doe"), ("Jane","Smith")
$myArray
# Append Data to the Array
$myArray += ("Sam","Smith")
$myArray

The output of this is shown in the following screenshot:

Картинка с сайта: www.packtpub.com

In this example, you add values to an existing array. You first start by defining an array of $myArray. You then print the existing contents of the array to the screen. You then add additional content by setting the array += to the new array data of ("Sam","Smith"). After reprinting the contents of the array to the screen, you see the values Sam and Smith added to the array.

Hashes

$users = @{"john.doe" = "jdoe"; "jane.doe" = "jdoe1"}
$users

$users = @{"john.doe" = "jdoe"; "jane.doe" = "jdoe1"}
$users["john.doe"]

$users = @{"john.doe" = "jdoe"; " jane.doe" = "jdoe1"}
$users
$users.add("John.Smith", "jsmith")
$users

$users = @{"john.doe" = "jdoe"; "jane.doe" = "jdoe1"}
$users
$users["jane.doe"] = "jadoe"
$users

$users = @{"john.doe" = "jdoe"; "jane.doe" = "jdoe1"}
$users
$users.remove("Jane.Doe")
$users

Deciding the best container for your scripts

• Math operations that require calculations of single or multiple values
• Catching single-line output from executing a non-PowerShell command
• Tracking current position in a loop like «percent complete»

• Storing a list of items for individual processing within a script
• Dumping error information from a PowerShell cmdlet

• Mapping data from one value to another value
• Data that requires frequent searching, updating, or building during script execution
• Storing multiple values of correlated data like user object attributes

Summary