Parameter attributes (Mandatory, ValidateSet) in PowerShell - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Mandatory attribute do in a PowerShell parameter?

The Mandatory attribute makes a parameter required. PowerShell will ask the user to provide a value if it is not supplied when running the script or function.

beginner

What is the purpose of the ValidateSet attribute in PowerShell parameters?

The ValidateSet attribute restricts the parameter's input to a predefined list of allowed values. This helps prevent errors by limiting choices to valid options.

intermediate

How do you define a mandatory parameter named Color that only accepts 'Red', 'Green', or 'Blue'?

Use [Parameter(Mandatory=$true)][ValidateSet('Red','Green','Blue')]$Color in the parameter block to make it required and limit choices.

beginner

What happens if a user provides a value not in the ValidateSet list?

PowerShell throws an error and stops execution, telling the user the value is invalid and showing the allowed options.

beginner

Can you combine Mandatory and ValidateSet attributes on the same parameter?

Yes, combining them ensures the parameter is required and only accepts specific values from the set.

What does the Mandatory attribute do in a PowerShell parameter?

A Validates the parameter type

B Limits the parameter to specific values

C Makes the parameter optional

D Makes the parameter required to be provided

The Mandatory attribute forces the user to provide a value for the parameter.

Which attribute restricts a parameter's input to a fixed list of values?

A Mandatory

B ValidateRange

C ValidateSet

D Parameter

ValidateSet limits input to a predefined set of allowed values.

What will happen if a user omits a parameter marked as Mandatory?

A PowerShell will assign a default value

B PowerShell will prompt the user to enter a value

C PowerShell will ignore the parameter

D PowerShell will throw an error immediately

PowerShell prompts the user to enter a value for mandatory parameters if missing.

If a parameter has ValidateSet('Red','Green','Blue'), what happens if the user inputs 'Yellow'?

A PowerShell throws an error about invalid value

B PowerShell ignores the parameter

C PowerShell converts 'Yellow' to 'Red'

D The script runs normally

PowerShell throws an error because 'Yellow' is not in the allowed set.

How do you make a parameter both required and limited to specific values?

A Use both <code>[Parameter(Mandatory=$true)]</code> and <code>[ValidateSet()]</code>

B Use <code>[ValidateSet()]</code> only

C Use <code>[Parameter(Mandatory=$true)]</code> only

D Use <code>[MandatorySet()]</code>

Combining both attributes makes the parameter required and restricts its values.

Explain how the Mandatory and ValidateSet attributes work together in PowerShell parameters.

Think about forcing the user to choose from specific options.

Describe what happens when a user runs a script without providing a mandatory parameter that has a ValidateSet.

Consider the user experience when input is missing or wrong.

Practice

1. What does the [Parameter(Mandatory=$true)] attribute do in a PowerShell script parameter?

easy

A. It limits the parameter to specific allowed values.

B. It sets a default value for the parameter.

C. It makes the parameter optional.

D. It makes the parameter required when running the script.

Solution

1. Step 1: Understand the Mandatory attribute

   The Mandatory=$true setting means the parameter must be provided by the user when running the script.

2. Step 2: Differentiate from other attributes

   Unlike ValidateSet, which restricts values, Mandatory only requires the parameter to be present.

3. Final Answer:

   It makes the parameter required when running the script. -> Option D

4. Quick Check:

   Mandatory = required parameter [OK]

Hint: Mandatory means you must provide the parameter value [OK]

Common Mistakes:

• Confusing Mandatory with ValidateSet
• Thinking Mandatory sets default values
• Assuming Mandatory makes parameter optional

2. Which of the following is the correct syntax to restrict a mandatory parameter to only accept the values 'Red', 'Green', or 'Blue' in PowerShell?

easy

A. [Parameter(Mandatory=$true)][ValidateSet('Red','Green','Blue')]$Color

B. [ValidateSet('Red','Green','Blue')][Parameter()]$Color

C. [Parameter()][ValidateSet('Red','Green','Blue')]$Color

D. [ValidateSet('Red','Green','Blue')]$Color

Solution

1. Step 1: Check attribute order and syntax

   Both Parameter and ValidateSet attributes can be used together. The order does not affect functionality, but the common style is to put Parameter first.

2. Step 2: Confirm Mandatory and ValidateSet usage

   [Parameter(Mandatory=$true)][ValidateSet('Red','Green','Blue')]$Color correctly uses Mandatory=$true and ValidateSet with the allowed values.

3. Final Answer:

   [Parameter(Mandatory=$true)][ValidateSet('Red','Green','Blue')]$Color -> Option A

4. Quick Check:

   Correct syntax = [Parameter(Mandatory=$true)][ValidateSet('Red','Green','Blue')]$Color [OK]

Hint: Use [Parameter()] before [ValidateSet()] for clarity [OK]

Common Mistakes:

• Swapping attribute order causing confusion
• Missing parentheses in ValidateSet
• Not setting Mandatory when required

3. Given the script snippet:

function Test-Color {
  param(
    [Parameter(Mandatory=$true)]
    [ValidateSet('Red','Green','Blue')]
    [string]$Color
  )
  Write-Output "Color chosen: $Color"
}

Test-Color -Color Yellow

What will happen when you run this script?

medium

A. It prompts the user to enter a valid color.

B. It outputs: Color chosen: Yellow

C. It throws a validation error because 'Yellow' is not in the ValidateSet.

D. It runs without error but ignores the color value.

Solution

1. Step 1: Understand ValidateSet behavior

   The ValidateSet attribute restricts input to the listed values only. 'Yellow' is not in the set 'Red', 'Green', 'Blue'.

2. Step 2: Predict script behavior on invalid input

   Passing 'Yellow' causes a validation error and stops the script before output.

3. Final Answer:

   It throws a validation error because 'Yellow' is not in the ValidateSet. -> Option C

4. Quick Check:

   ValidateSet blocks invalid values [OK]

Hint: ValidateSet blocks values not listed [OK]

Common Mistakes:

• Assuming script prompts instead of erroring
• Thinking it ignores invalid values
• Confusing Mandatory with ValidateSet behavior

4. You wrote this parameter declaration:

param(
  [Parameter(Mandatory=$true)]
  [ValidateSet('Small','Medium','Large')]
  [string]$Size
)

But when running the script without the -Size argument, it does not prompt for input and continues silently. What is the likely cause?

medium

A. The parameter type should be [int] instead of [string].

B. The script is missing CmdletBinding() to enable parameter validation.

C. Mandatory parameters never prompt for input automatically.

D. The ValidateSet attribute is incorrect and disables Mandatory.

Solution

1. Step 1: Understand Mandatory prompt behavior

   Mandatory parameters prompt for input only if the function or script uses CmdletBinding() or is an advanced function.

2. Step 2: Identify missing CmdletBinding()

   Without CmdletBinding(), the script treats parameters as simple variables and does not enforce Mandatory prompts.

3. Final Answer:

   The script is missing CmdletBinding() to enable parameter validation. -> Option B

4. Quick Check:

   CmdletBinding() enables Mandatory prompts [OK]

Hint: Add CmdletBinding() to enable Mandatory prompts [OK]

Common Mistakes:

• Thinking ValidateSet disables Mandatory
• Assuming Mandatory never prompts
• Changing parameter type unnecessarily

5. You want to create a script parameter that is required and only accepts the values 'Start', 'Stop', or 'Restart'. Which of the following parameter declarations correctly enforces both requirements and will prompt the user if the parameter is missing?

hard

A. [CmdletBinding()]
param(
[Parameter(Mandatory=$true)]
[ValidateSet('Start','Stop','Restart')]
[string]$Action
)

B. param(
[Parameter()]
[ValidateSet('Start','Stop','Restart')]
[string]$Action = 'Start'
)

C. [CmdletBinding()]
param(
[Parameter()]
[ValidateSet('Start','Stop','Restart')]
[string]$Action
)

D. param(
[Parameter(Mandatory=$true)]
[string]$Action
)

Solution

1. Step 1: Ensure Mandatory prompts user

   To prompt the user when a parameter is missing, the script must use CmdletBinding() and set Mandatory=$true.

2. Step 2: Restrict values with ValidateSet

   Using ValidateSet limits input to the allowed values 'Start', 'Stop', or 'Restart'.

3. Step 3: Check all options

   [CmdletBinding()] param( [Parameter(Mandatory=$true)] [ValidateSet('Start','Stop','Restart')] [string]$Action ) includes CmdletBinding(), Mandatory=$true, and ValidateSet, fulfilling all requirements.

4. Final Answer:

   [CmdletBinding()] param( [Parameter(Mandatory=$true)] [ValidateSet('Start','Stop','Restart')] [string]$Action ) -> Option A

5. Quick Check:

   CmdletBinding + Mandatory + ValidateSet = [CmdletBinding()] param( [Parameter(Mandatory=$true)] [ValidateSet('Start','Stop','Restart')] [string]$Action ) [OK]

Hint: Use CmdletBinding with Mandatory and ValidateSet together [OK]

Common Mistakes:

• Omitting CmdletBinding() so no prompt occurs
• Setting default value disables Mandatory prompt
• Not using ValidateSet to restrict values