Parameters in PowerShell

Introduction

Parameters let you give information to a script or function so it can work with different data each time.

You want to reuse a script but with different input values.

You need to make your script flexible for different tasks.

You want to avoid changing the script code every time you run it.

You want to make your script easier to understand by naming inputs clearly.

Syntax

PowerShell

param(
    [type]$ParameterName
)

Parameters are declared at the start of a script or function using param().

You can specify the type of the parameter to help catch errors early.

Examples

This script takes one string parameter called Name and prints a greeting.

PowerShell

param(
    [string]$Name
)

Write-Output "Hello, $Name!"

This script takes an integer parameter Count and prints numbers from 1 to that count.

PowerShell

param(
    [int]$Count
)

for ($i = 1; $i -le $Count; $i++) {
    Write-Output "Number $i"
}

This script has a parameter with a default value. If no value is given, it uses "default.txt".

PowerShell

param(
    [string]$FilePath = "default.txt"
)

Write-Output "Processing file: $FilePath"

Sample Program

This script takes two parameters: a user name and an age, then prints them.

PowerShell

param(
    [string]$UserName,
    [int]$Age
)

Write-Output "User Name: $UserName"
Write-Output "User Age: $Age"

Important Notes

You run the script by passing parameters like: .\script.ps1 -UserName Alice -Age 30.

If you don't provide a parameter value and no default is set, PowerShell will ask you to enter it.

Using parameters makes your scripts more reusable and easier to maintain.

Summary

Parameters let scripts accept input values to work with.

Declare parameters at the start using param().

You can set types and default values for parameters.

Practice

1. What is the purpose of using param() in a PowerShell script?

easy

A. To declare input parameters that the script can accept

B. To define a function inside the script

C. To output results from the script

D. To comment lines in the script

Solution

1. Step 1: Understand the role of param()

   The param() block is used at the start of a PowerShell script to declare parameters that the script can accept as input.

2. Step 2: Differentiate from other script parts

   It is not used to define functions, output results, or comment lines. Those have different syntax and purposes.

3. Final Answer:

   To declare input parameters that the script can accept -> Option A

4. Quick Check:

   param() declares input parameters [OK]

Hint: Remember: param() is for input, not output or comments [OK]

Common Mistakes:

• Confusing param() with function declaration
• Thinking param() outputs data
• Using param() to comment code

2. Which of the following is the correct syntax to declare a mandatory string parameter named Name in PowerShell?

easy

A. param([string]$Name = "")

B. param([string]$Name)

C. param($Name:string Mandatory)

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

Solution

1. Step 1: Understand mandatory parameter syntax

   To make a parameter mandatory, use the [Parameter(Mandatory=$true)] attribute before the type and name.

2. Step 2: Check each option

   param([Parameter(Mandatory=$true)][string]$Name) correctly uses [Parameter(Mandatory=$true)][string]$Name. param([string]$Name = "") sets a default empty string, so not mandatory. param([string]$Name) lacks the mandatory attribute. param($Name:string Mandatory) is invalid syntax.

3. Final Answer:

   param([Parameter(Mandatory=$true)][string]$Name) -> Option D

4. Quick Check:

   Mandatory parameter needs [Parameter(Mandatory=$true)] [OK]

Hint: Mandatory parameters use [Parameter(Mandatory=$true)] attribute [OK]

Common Mistakes:

• Omitting the Mandatory attribute
• Using default value instead of mandatory
• Incorrect attribute syntax

3. What will be the output of this script when run with -Count 3?

param([int]$Count = 1)
for ($i = 1; $i -le $Count; $i++) { Write-Output "Number $i" }

medium

A. Number 1
Number 2
Number 3

B. Number 1

C. Number 3

D. Error: Missing parameter

Solution

1. Step 1: Understand parameter default and input

   The parameter $Count has a default of 1 but is overridden by passing -Count 3.

2. Step 2: Trace the loop output

   The for loop runs from 1 to 3, outputting "Number 1", "Number 2", and "Number 3" each on a new line.

3. Final Answer:

   Number 1 Number 2 Number 3 -> Option A

4. Quick Check:

   Loop runs 3 times with Count=3 [OK]

Hint: Parameter overrides default; loop runs Count times [OK]

Common Mistakes:

• Ignoring passed parameter and using default
• Expecting single output instead of looped output
• Confusing parameter name or type

4. Identify the error in this parameter declaration:

param([int]$Age = "twenty")

medium

A. Missing mandatory attribute

B. Type mismatch: assigning string to int parameter

C. Parameter name cannot be Age

D. Default value must be null

Solution

1. Step 1: Check parameter type and default value

   The parameter $Age is declared as [int] but the default value is the string "twenty".

2. Step 2: Understand type mismatch error

   PowerShell cannot convert the string "twenty" to an integer, causing a type mismatch error.

3. Final Answer:

   Type mismatch: assigning string to int parameter -> Option B

4. Quick Check:

   Default value must match parameter type [OK]

Hint: Default values must match declared parameter type [OK]

Common Mistakes:

• Assigning string default to int parameter
• Ignoring type mismatch errors
• Assuming parameter name restrictions

5. You want to create a script that accepts two parameters: Path (string, mandatory) and Verbose (switch, optional). Which is the correct way to declare these parameters?

hard

A. param([string]$Path, [Parameter(Mandatory=$true)][switch]$Verbose)

B. param([string]$Path = "", [switch]$Verbose = $false)

C. param([Parameter(Mandatory=$true)][string]$Path, [switch]$Verbose)

D. param([switch]$Path, [string]$Verbose)

Solution

1. Step 1: Identify mandatory and optional parameters

   Path must be mandatory string, so use [Parameter(Mandatory=$true)][string]$Path. Verbose is an optional switch, so [switch]$Verbose without mandatory attribute.

2. Step 2: Evaluate each option

   param([Parameter(Mandatory=$true)][string]$Path, [switch]$Verbose) correctly declares Path as mandatory string and Verbose as optional switch. param([string]$Path, [Parameter(Mandatory=$true)][switch]$Verbose) wrongly makes Verbose mandatory. param([string]$Path = "", [switch]$Verbose = $false) sets default empty string for Path, so not mandatory. param([switch]$Path, [string]$Verbose) swaps types incorrectly.

3. Final Answer:

   param([Parameter(Mandatory=$true)][string]$Path, [switch]$Verbose) -> Option C

4. Quick Check:

   Mandatory string + optional switch = param([Parameter(Mandatory=$true)][string]$Path, [switch]$Verbose) [OK]

Hint: Mandatory uses [Parameter(Mandatory=$true)], switches don't [OK]

Common Mistakes:

• Making switches mandatory
• Setting default values instead of mandatory
• Mixing parameter types