Assign values and types to variables in Windows PowerShell scripts
When working with variable values, you use the standard mathematical operators that you're already familiar with, such as equal (=), plus (+), and minus (–).
To assign a value to a variable, you use the equal (=) operator. For example:
$num1 = 10
$logFile = "C:\Logs\log.txt"
You can also assign a value to a variable by using a command that's evaluated. The result of the command is placed in the variable. For example:
$user = Get-ADUser Administrator
$service = Get-Service W32Time
Note
If a command returns multiple results, then the variable becomes an array containing multiple values. You'll learn about arrays later in this module.
You can display the value of a variable by entering the variable name and then pressing the Enter key. You can also display the value as part of a command by using Write-Host. For example:
$user
Write-Host "The location of the log file is $logFile"
Note
When you display a variable by using Write-Host and you place the variable name in double quotes ("), that variable is evaluated and its value is displayed. If you use single quotes ('), that variable isn't evaluated, resulting in its name being displayed instead.
Note
Write-Host sends output directly to the console and bypasses the PowerShell pipeline. Output written with Write-Host can't be captured in a variable or piped to another command. For pipeline-compatible output, use Write-Output or simply enter the variable name on its own line.
To remove all values from a variable, you can set the variable equal to $null. The $null variable is automatically defined by PowerShell as nothing. For example:
$num1 = $null
$str1 = $null
Note
To clear a variable, you can also use Clear-Variable.
You can use mathematical operators with variables, as the following example depicts:
$area = $length * $width
$sum = $num1 + $num2
$path = $folder + $file
You can set the value of a variable by using the Set-Variable cmdlet. When you use this cmdlet, you don't include the $ symbol when referring to the name, as the following example depicts:
Set-Variable -Name num1 -Value 5
PowerShell also supports compound assignment operators that combine an operation with assignment in a single step. For example, $count += 1 is equivalent to $count = $count + 1. Other compound operators include -=, *=, and the increment (++) and decrement (--) operators.
Additional reading: For more information about assignment operators, refer to about_Assignment_Operators.
Assigning a type to a variable
PowerShell assigns a type to all variables. The variable type determines the data that can be stored in it. In most cases, PowerShell automatically determines the type of a variable during assignment of its value. Automatic assignment of the variable type works well most of the time. However, in some cases, the data type is ambiguous, and you might prefer to set the variable type explicitly.
The following table lists the common variable types used in PowerShell.
Table 1: Common variable types used in PowerShell
| Type | Description |
|---|---|
| String | A string variable stores text that can include special characters. For example, "This is a string." |
| Int | A 32-bit integer variable stores a number without decimal places. For example, 228. |
| Double | A 64-bit floating point variable stores a number that can include decimal places. For example, 128.45. |
| DateTime | A DateTime variable stores a date object that includes a date and time. For example, January 5, 2022 10:00 AM. |
| Bool | A Boolean variable can store only the values $true or $false. |
If you don't assign a variable type, PowerShell assigns a type automatically based on the value you assign to the variable. When the value is contained in quotes, it's generally interpreted as a string. For example, PowerShell would interpret 5 as an integer, but "5" as a string.
You can force a variable to accept only a specific type of content by defining the type. When you define the type, PowerShell attempts to convert the value you provide into the correct type. If PowerShell can't convert the value into the correct type, it returns an error.
The following examples depict the $num2 variable being defined as a 32-bit integer and the $date variable being defined as DateTime.
[Int]$num2 = "5"
[DateTime]$date = "January 5, 2022 10:00AM"
You can review a variable's type by appending the GetType() method to the name of the variable. For example:
$date.GetType()