Set-StrictMode

Syntax

Set-StrictMode
   -Version <Version>
   [<CommonParameters>]

Set-StrictMode
   [-Off]
   [<CommonParameters>]

Description

The Set-StrictMode cmdlet configures strict mode for the current scope and all child scopes, and turns it on and off. When strict mode is on, PowerShell generates a terminating error when the content of an expression, script, or script block violates basic best-practice coding rules.

Use the Version parameter to determine the coding rules to enforce.

Set-PSDebug -Strict cmdlet turns on strict mode for the global scope. Set-StrictMode affects only the current scope and its child scopes. Then, you can use it in a script or function to override the setting inherited from the global scope.

When Set-StrictMode is off, PowerShell has the following behaviors:

• Uninitialized variables are assumed to have a value of 0 (zero) or $Null, depending on type
• References to non-existent properties return $Null
• Results of improper function syntax vary with the error conditions
• Attempting to retrieve a value using an invalid index in an array returns $Null

Examples

Example 1: Turn on strict mode as version 1.0

# Strict mode is off by default.
$a -gt 5

False

Set-StrictMode -Version 1.0
$a -gt 5

InvalidOperation: The variable '$a' cannot be retrieved because it has not been set.

With strict mode set to version 1.0, attempts to reference variables that aren't initialized fail.

Example 2: Turn on strict mode as version 2.0

# Strict mode is off by default.
function add ($a, $b) {
    '$a = ' + $a
    '$b = ' + $b
    '$a+$b = ' + ($a + $b)
}
add 3 4

$a = 3
$b = 4
$a+$b = 7

add(3,4)

$a = 3 4
$b =
$a+$b = 3 4

Set-StrictMode -Version 2.0
add(3,4)

InvalidOperation: The function or command was called as if it were a method. Parameters should be separated by spaces. For information about parameters, see the about_Parameters Help topic.

Set-StrictMode -Off
$string = "This is a string."
$null -eq $string.Month

True

Set-StrictMode -Version 2.0
$string = "This is a string."
$null -eq $string.Month

PropertyNotFoundException: The property 'Month' cannot be found on this object. Verify that the property exists.

This command turns strict mode on and sets it to version 2.0. As a result, PowerShell returns an error if you use method syntax, which uses parentheses and commas, for a function call or reference uninitialized variables or non-existent properties.

The sample output shows the effect of version 2.0 strict mode.

Without version 2.0 strict mode, the (3,4) value is interpreted as a single array object to which nothing is added. With version 2.0 strict mode, it's correctly interpreted as faulty syntax for submitting two values.

Without version 2.0, the reference to the non-existent Month property of a string returns only $Null. With version 2.0, it's interpreted correctly as a reference error.

Example 3: Turn on strict mode as version 3.0

With strict mode set to Off, invalid or out of bounds indexes result return null values.

# Strict mode is off by default.
$a = @(1)
$null -eq $a[2]
$null -eq $a['abc']

True
True

Set-StrictMode -Version 3.0
$a = @(1)
$null -eq $a[2]
$null -eq $a['abc']

OperationStopped: Index was outside the bounds of the array.

InvalidArgument: Cannot convert value "abc" to type "System.Int32". Error: "Input string was not in a correct format."

With strict mode set to version 3 or higher, invalid or out of bounds indexes result in errors.

Parameters

-Off

-Version

Inputs

None

You can't pipe objects to this cmdlet.

Outputs

None

This cmdlet returns no output.

Notes

While the Version parameter accepts values greater than 3.0, there are no additional rules defined for anything higher than 3.0.

Set-StrictMode is effective only in the scope it's set in and in its child scopes. For more information about scopes in PowerShell, see about_Scopes.

Related Links

• Set-PSDebug