Parameter validation in PowerShell - Mini Project: Build & Apply

Parameter validation

📖 Scenario: You are creating a PowerShell script that accepts user input as parameters. To make sure the input is correct and safe, you will add parameter validation rules.This is like checking the ingredients before cooking to ensure the recipe works well.

🎯 Goal: Build a PowerShell script with parameters that have validation rules to accept only specific types and values.

📋 What You'll Learn

Create a script with a parameter named Name that accepts only strings.

Add a parameter named Age that accepts only integers between 18 and 99.

Add a parameter named Country that accepts only specific values: 'USA', 'Canada', or 'UK'.

Print the received parameter values.

💡 Why This Matters

🌍 Real World

Parameter validation helps prevent errors and ensures scripts run with correct input, just like checking ingredients before cooking.

💼 Career

Many IT and automation jobs require writing scripts that safely accept user input. Parameter validation is a key skill for reliable scripts.

1

Create parameters Name and Age

Write a PowerShell script that defines two parameters: Name which accepts only strings, and Age which accepts only integers.

PowerShell

param(
    # Define parameter Name as string
    # Define parameter Age as int
)

# Your code here

Hint

Use [string] and [int] before the parameter names inside param().

2

Add validation for Age to accept only 18 to 99

Modify the Age parameter to accept only integers between 18 and 99 using [ValidateRange(18, 99)].

PowerShell

param(
    [string]$Name,
    # Add ValidateRange to Age
    [int]$Age
)

# Your code here

Hint

Use [ValidateRange(18, 99)] just before [int]$Age.

3

Add parameter Country with specific allowed values

Add a new parameter called Country that accepts only the values 'USA', 'Canada', or 'UK' using [ValidateSet('USA', 'Canada', 'UK')] and type string.

PowerShell

param(
    [string]$Name,
    [ValidateRange(18, 99)]
    [int]$Age,
    # Add Country parameter with ValidateSet
)

# Your code here

Hint

Use [ValidateSet('USA', 'Canada', 'UK')] before [string]$Country.

4

Print the parameter values

Write code to print the values of Name, Age, and Country using Write-Host.

PowerShell

param(
    [string]$Name,
    [ValidateRange(18, 99)]
    [int]$Age,
    [ValidateSet('USA', 'Canada', 'UK')]
    [string]$Country
)

# Print Name, Age, and Country
# Your code here

Hint

Use Write-Host to display each parameter value on its own line.

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