PowerShell uses assignment operators to set values to variables. We've been using the equal sign, but there are many other operators as well. Table 6.3 lists PowerShell assignment operators:
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Operator | Description |
---|---|
= | Sets a value of a variable to the specified value. |
+= | Increases the value of a variable by the specified value or appends to the existing value. |
-= | Decreases the value of a variable by the specified value. |
*= | Multiplies the value of a variable by the specified value or appends to the existing value. |
/= | Divides the value of a variable by the specified value. |
%= | Divides the value of a variable by the specified value and assigns the remainder (modulus) to the variable. |
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In addition to the traditional uses of =, in PowerShell this operator has a few extra bells and whistles that might be of interest to you. First, when you assign a hexadecimal value to a variable, it is stored as its decimal equivalent:
PS C:\> $var=0x10 PS C:\> $var 16 PS C:\>
You can also use a type of shorthand to assign a variable a multiple byte value. By using kb, mb, and gb, which are known as numeric constants, you store actual kilobyte, megabyte, and gigabyte values respectively:
PS C:\> $var=10KB PS C:\> $var 10240 PS C:\> $var=2MB PS C:\> $var 2097152 PS C:\> $var=.75GB PS C:\> $var 805306368 PS C:\>
In the first example we set $var to 10KB or 10 kilobytes. Displaying the contents of $var shows the actual byte value of 10 kilobytes. We repeat the process by setting $var to 2 megabytes and then .75 gigabytes. In each example we display the value of $var. By the way, there is no numeric constant for a terabyte.
The += operator increases the value of a given variable by a specified amount:
PS C:\> $var=7 PS C:\> $var 7 PS C:\> $var+=3 PS C:\> $var 10 PS C:\>
The variable $var begins with a value of 7. We then use += to increment it by 3, which changes the value of $var to 10.
The -= operator decreases the value of a given variable by a specified amount. Let's continue with the previous example:
PS C:\> $var-=3 PS C:\> $var 7 PS C:\>
$var starts out with a value of 10. Using the -= operator we decrease its value by 3, which returns us to 7.
What if we want to multiply a variable value by a specific number? This calls for the *= operator. Let's continue with the same $var that currently has a value of 7:
PS C:\> $var*=3 PS C:\> $var 21 PS C:\>
We can also divide by use the /= operator:
PS C:\> $var/=7 PS C:\> $var 3 PS C:\>
Finally, we can use %= to divide the variable value by the assigned value and return the modulus or remainder:
PS C:\> $var=9 PS C:\> $var%=4 PS C:\> $var 1 PS C:\>
In this example we start with a $var value of 9. Using the modulus assignment operator with a value of 4 means we're diving 9 into 4. The remainder value is then assigned to $var, which in this example is 1.
You need to be careful with assignment operators and variable values. Remember PowerShell does a pretty good job at deciding if what you typed is a number or a string. If you put something in quotes PowerShell treats it as a string. If you're not careful, you can get some odd results:
PS C:\> $var="3" PS C:\> $var+=7 PS C:\> $var 37 PS C:\>
In this example we think we set $var to 3 and increased it by 7 using the += operator. However, "3" is a string, so the += operator simply concatenates instead of adds, which is why we end up with a $var value of 37. If you are ever unsure about what type of object you're working with, you can use GetType():
PS C:\> $var.gettype() IsPublic IsSerial Name BaseType -------- -------- ---- -------- True True String System.Object PS C:\>
One final comment on assignment operators: It is possible to assign values to multiple variables with a single statement:
PS C:\> $varA,$varB,$varC="Apple",3.1416,"Windows" PS C:\> get-variable var? Name Value ---- ----- varC Windows varB 3.1416 varA Apple PS C:\>
The assigned values are set to their respective variables. If you have more values than variables, then the extra values are assigned to the last variable:
PS C:\> $varA,$varB,$varC="Apple",3.1416,"Windows","Linux" PS C:\> get-variable var? Name Value ---- ----- varC {Windows, Linux} varB 3.1416 varA Apple PS C:\>
Our recommendation is to be careful with this type of statement since you can end up with unintentional variable values. PowerShell will wait, so set and modify variables one at a time.