Parameter validation in PowerShell - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this PowerShell function call with parameter validation?

Consider the following PowerShell function that validates its parameter. What will be the output when calling Test-Param -Number 15?

PowerShell

function Test-Param {
  param(
    [ValidateRange(1,10)]
    [int]$Number
  )
  "Number is $Number"
}

Test-Param -Number 15

A No output, function silently ignores invalid input

B Number is 15

C ValidationException: Cannot validate argument on parameter 'Number'. The argument 15 is less than the minimum allowed range of 1.

D ValidationException: Cannot validate argument on parameter 'Number'. The argument 15 is greater than the maximum allowed range of 10.

💡 Hint

Think about what happens when a parameter value is outside the allowed range in PowerShell parameter validation.

The function uses [ValidateRange(1,10)] which restricts the parameter to values between 1 and 10. Passing 15 violates this, causing a ValidationException with a message about exceeding the maximum allowed range.

💻 Command Output

intermediate

What error does this PowerShell function produce when called with an invalid string?

Given this function with parameter validation, what error message appears when calling Check-Name -Name 'John123'?

PowerShell

function Check-Name {
  param(
    [ValidatePattern('^[a-zA-Z]+$')]
    [string]$Name
  )
  "Name is $Name"
}

Check-Name -Name 'John123'

A ValidationException: Cannot validate argument on parameter 'Name'. The argument 'John123' does not match the pattern '^[a-zA-Z]+$'.

B No output, function returns null

C RuntimeException: Invalid characters in parameter 'Name'.

D Name is John123

💡 Hint

Look at the regex pattern used in ValidatePattern and what input is given.

The pattern '^[a-zA-Z]+$' allows only letters. 'John123' contains digits, so it fails validation and throws a ValidationException with a message about the pattern mismatch.

📝 Syntax

advanced

Which option correctly uses ValidateSet to restrict parameter values?

You want to create a function parameter that only accepts the values 'Red', 'Green', or 'Blue'. Which of the following parameter declarations is correct?

PowerShell

function Set-Color {
  param(
    # Parameter declaration here
  )
  "Color set to $Color"
}

A

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

B

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

C

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

D

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

💡 Hint

Think about the data type that matches color names.

ValidateSet restricts the parameter to specific string values. The parameter type must be string to accept color names. Using int, bool, or array types will cause errors or unexpected behavior.

🚀 Application

advanced

What is the output of this function when called with -Age 25?

This function uses multiple parameter validations. What will it output when called as Check-Age -Age 25?

PowerShell

function Check-Age {
  param(
    [ValidateRange(18,30)]
    [ValidateNotNull()]
    [int]$Age
  )
  if ($Age -ge 21) {
    "Adult"
  } else {
    "Young Adult"
  }
}

Check-Age -Age 25

A Adult

B Young Adult

C ValidationException: Age is out of range

D No output

💡 Hint

Check the range and the if condition inside the function.

The parameter Age is validated to be between 18 and 30 and not null. 25 passes validation. Since 25 is greater or equal to 21, the function outputs 'Adult'.

🧠 Conceptual

expert

Which parameter validation attribute prevents null or empty strings?

You want to ensure a string parameter is not null or empty in your PowerShell function. Which validation attribute should you use?

A [ValidateNotNull()]

B [ValidateNotEmpty()]

C [ValidateNotNullOrEmpty()]

D [ValidateString()]

💡 Hint

One attribute specifically checks for both null and empty strings.

[ValidateNotNull()] only prevents null values but allows empty strings. [ValidateNotNullOrEmpty()] prevents both null and empty strings. The other options are not valid PowerShell validation attributes.

Practice

1. What is the main purpose of parameter validation in a PowerShell script?

easy

A. To speed up the script execution

B. To format the output of the script

C. To check input values before the script runs to avoid errors

D. To create new variables automatically

Solution

1. Step 1: Understand parameter validation role

   Parameter validation ensures inputs meet certain rules before the script runs.

2. Step 2: Identify the main benefit

   This prevents errors caused by bad inputs and makes scripts safer.

3. Final Answer:

   To check input values before the script runs to avoid errors -> Option C

4. Quick Check:

   Parameter validation = input checking [OK]

Hint: Validation checks inputs early to prevent errors [OK]

Common Mistakes:

• Thinking validation speeds up script
• Confusing validation with output formatting
• Assuming validation creates variables

2. Which of the following is the correct syntax to validate that a parameter only accepts values from a fixed set: 'Red', 'Green', or 'Blue'?

easy

A. [ValidateSet('Red','Green','Blue')] param([string]$Color)

B. [ValidateRange('Red','Green','Blue')] param([string]$Color)

C. [ValidateNotNullOrEmpty('Red','Green','Blue')] param([string]$Color)

D. [ValidatePattern('Red|Green|Blue')] param([string]$Color)

Solution

1. Step 1: Identify correct validation attribute for fixed sets

   [ValidateSet] restricts input to specific allowed values.

2. Step 2: Match syntax with attribute usage

   The syntax [ValidateSet('Red','Green','Blue')] is correct for this purpose.

3. Final Answer:

   [ValidateSet('Red','Green','Blue')] param([string]$Color) -> Option A

4. Quick Check:

   Fixed set validation = ValidateSet [OK]

Hint: Use ValidateSet for fixed allowed values [OK]

Common Mistakes:

• Using ValidateRange for strings
• Confusing ValidateNotNullOrEmpty with value restriction
• Using ValidatePattern incorrectly for sets

3. What will be the output of this script if called with -Age 25?

function Test-Age {
  param(
    [ValidateRange(18,30)]
    [int]$Age
  )
  "Age is $Age"
}
Test-Age -Age 25

medium

A. "Age is 18"

B. Error: Parameter validation failed

C. No output

D. "Age is 25"

Solution

1. Step 1: Check parameter validation range

   The parameter $Age must be between 18 and 30 inclusive.

2. Step 2: Verify input against range

   Input 25 is within the range, so validation passes and script runs.

3. Final Answer:

   "Age is 25" -> Option D

4. Quick Check:

   25 in 18-30 range = valid input [OK]

Hint: Check if input fits ValidateRange limits [OK]

Common Mistakes:

• Assuming validation fails for valid input
• Confusing output with error message
• Ignoring the inclusive range

4. Identify the error in this parameter validation code:

function Set-Name {
  param(
    [ValidateNotNullOrEmpty()]
    [string]$Name
  )
  "Name set to $Name"
}
Set-Name -Name $null

medium

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

B. The function will throw a validation error because $Name is null

C. The ValidateNotNullOrEmpty attribute is used incorrectly without parameters

D. The function will accept null and print 'Name set to '

Solution

1. Step 1: Understand ValidateNotNullOrEmpty behavior

   This attribute rejects null or empty string inputs.

2. Step 2: Analyze input value

   The input is $null, which violates the validation rule, causing an error.

3. Final Answer:

   The function will throw a validation error because $Name is null -> Option B

4. Quick Check:

   Null input with ValidateNotNullOrEmpty = error [OK]

Hint: Null or empty inputs fail ValidateNotNullOrEmpty [OK]

Common Mistakes:

• Thinking null is accepted
• Assuming ValidateNotNullOrEmpty needs parameters
• Confusing parameter type requirements

5. You want to create a script parameter $Port that only accepts integers between 1024 and 65535 and cannot be empty. Which parameter validation attributes should you use together?

hard

A. [ValidateRange(1024,65535)][ValidateNotNullOrEmpty()]

B. [ValidateSet(1024,65535)][ValidateNotNullOrEmpty()]

C. [ValidatePattern('^[0-9]{4,5}$')]

D. [ValidateNotNullOrEmpty()][ValidateLength(4,5)]

Solution

1. Step 1: Choose attribute for numeric range

   [ValidateRange(1024,65535)] ensures the integer is within the port number range.

2. Step 2: Ensure parameter is not empty

   [ValidateNotNullOrEmpty()] prevents null or empty input.

3. Step 3: Combine both for full validation

   Using both attributes together enforces the correct range and non-empty input.

4. Final Answer:

   [ValidateRange(1024,65535)][ValidateNotNullOrEmpty()] -> Option A

5. Quick Check:

   Range + NotNullOrEmpty = correct port validation [OK]

Hint: Combine ValidateRange and ValidateNotNullOrEmpty for numeric required input [OK]

Common Mistakes:

• Using ValidateSet for numeric ranges
• Relying on ValidatePattern for numeric range checks
• Missing non-empty validation