Arrays in PowerShell – Create, change, read, sort, delete

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Wolfgang Sommergut

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Unlike in strongly typed languages, such as C or Java, in PowerShell you don’t have to declare a variable as an array. It is sufficient to add values in the correct way to automatically transform a variable into an array. However, one exception is handling arrays that you want to restrict to one data type.

Work with data types

By default, PowerShell assumes that the elements of an array are of the type variant. This means that you can mix different data types—that is, combine numerical values, dates, or strings in a single variable. However, if you want to restrict an array to a certain data type, you can declare the array in the following way:

[int[]] $e = 1,2,3,4,5,6,7,8,9

Notice that a mere declaration is insufficient. You also have to assign values to the variable. If the data types don’t match, PowerShell will throw an error.

An elegant alternative for assigning consecutive numerical values is the use of the range operator, which allows you to simplify the above command:

[int[]] $e = 1 .. 9

Assign values to an array

The first example demonstrates how to explicitly assign values to an array using the so-called simplified syntax. An alternative would be:

$colors = @("black","white","yellow","blue")

Under normal circumstances, you would want to avoid the additional effort of this notation. However, it helps you understand why you can create an empty array in PowerShell with this command:

$colors = @()

In many cases, you won’t assign values manually to an array. Instead, you will want to store the output of a cmdlet in a variable. If the output is an array, it can be tested like this:

(Get-Process) -is [array]

If you only want to store specific properties in the variables, and not the entire output of the command, you can filter the properties with the Select-Object:

$mac = Get-NetAdapter | Select MacAddress

This command would save all MAC addresses of the installed NICs in the variable $mac.

Add elements to an array

If you later want to add elements to an array, you don’t have to call a method because the operator “+” is used for this purpose.

$colors = $colors + "orange"

Or, if you want to use the combined assignment operator, you can rewrite the above example like this:

$colors += "orange"

You can also combine two arrays this way. For instance, if you have another array $pattern with the values “dotted,” “checked,” and “lined,” you could concatenate it to $colors with this command:

$colors += $pattern

Display the contents of an array

If you want to display the elements of an array, you usually don’t need a loop. In the simplest case, it is enough to enter the variable name to make PowerShell display all values of the array.

As in other programming languages, you can access a specific element though the index. As expected,

$colors[0]

displays “black.” It is important to note that, contrary to some BASIC dialects, PowerShell starts counting at zero. PowerShell not only accepts a single index value but also accepts constructs like this:

$colors[1,4,7]

This command would display the array’s second, fifth, and eighth element. You can also use the range operator if you want to display a connected range:

$colors[2 .. 6]

Negative numbers allow you to access the last elements of the array. For instance, this command would display the last element:

$colors[-1]

Correspondingly, -2 would display the next-to-last element.

Find elements

If you want to determine if an array contains a certain value, you don’t have to iterate through elements to compare them with the search term. Rather, you can apply various comparison operators directly to the array.

$colors[0 .. 5] -like "*ck*"

This command would find “black” and “checked.”

Sort arrays

Arranging the elements of an array in a certain order is fairly easy with PowerShell. All you have to do is pipe the output of an array to the Sort-Object cmdlet:

$colors | Sort

Of course, you can leverage the extensive features of the Sort-Object, such as changing the sort order to descending or removing duplicates.

If you want to sort the order not just to display it on the screen but also to store it in the array, you have to assign the elements again:

$colors = $colors | Sort

Delete arrays and elements

Even though most of the array operations in PowerShell are relatively easy to accomplish, no convincing solution exists for removing specific elements or deleting complete arrays. The easiest way to get rid of an entire array is to assign the variable $null:

$colors = $null

If you want to remove specific elements, you need a workaround that filters and reassigns values.

$colors = $colors | where {$_ -ne "yellow"}

In this example, the Where-Object would return all elements that are unequal to “yellow” and assign them to the array. The result is that the element with the value “yellow” is removed from the array.