Mandatory Parameters¶

Mandatory parameters are parameters that must be supplied when calling a function. If the caller does not provide a value, PowerShell automatically prompts for it. Mandatory parameters are essential when a function cannot run correctly without specific input.

Mandatory parameters are defined using the [Parameter(Mandatory = $true)] attribute inside the param() block.

1. Basic Syntax for Mandatory Parameters¶

The general structure is:

function Name {
    param(
        [Parameter(Mandatory = $true)]
        $ParameterName
    )

    <code>
}

• The [Parameter()] attribute modifies how the parameter behaves.
• Mandatory = $true tells PowerShell that the parameter is required.

2. Example: A Function With One Mandatory Parameter¶

function Show-Message {
    param(
        [Parameter(Mandatory = $true)]
        $Text
    )

    "Message: $Text"
}

Show-Message

Explanation:

• The function requires a value for $Text.
• Calling Show-Message without arguments triggers an interactive prompt:

cmdlet Show-Message at command pipeline position 1
Supply values for the following parameters:
Text:

The user must enter a value before the function runs.

3. Mandatory Parameters With Named Arguments¶

You can call the function using the parameter name:

Show-Message -Text "Hello"

This runs without prompting because the required parameter is supplied.

4. Multiple Mandatory Parameters¶

You can mark more than one parameter as mandatory.

function Add-Numbers {
    param(
        [Parameter(Mandatory = $true)]
        [int]$A,

        [Parameter(Mandatory = $true)]
        [int]$B
    )

    $A + $B
}

Calling without both values:

Add-Numbers

PowerShell prompts for both $A and $B.

Calling with values:

Add-Numbers -A 5 -B 7

Returns:

12

5. Mandatory Parameters With Type Conversion¶

Mandatory parameters still support type conversion:

function Multiply {
    param(
        [Parameter(Mandatory = $true)]
        [int]$X,

        [Parameter(Mandatory = $true)]
        [int]$Y
    )

    $X * $Y
}

Multiply -X "3" -Y "4"

Explanation:

• "3" and "4" are strings.
• PowerShell converts them to integers.
• The function returns 12.

If conversion fails, PowerShell stops and reports an error.

6. Mandatory Parameters With Validation¶

Mandatory parameters can also use validation attributes.

function Set-Age {
    param(
        [Parameter(Mandatory = $true)]
        [ValidateRange(1,120)]
        [int]$Age
    )

    "Age set to $Age"
}

Calling:

Set-Age

PowerShell prompts for $Age.

If the user enters 200, validation fails and PowerShell displays an error.

7. Mandatory Parameters and Pipeline Input¶

Mandatory parameters can also accept pipeline input.

If the pipeline does not supply a value, PowerShell prompts for it.

function Show-Item {
    param(
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        $Item
    )

    "Item: $Item"
}

"apple","banana" | Show-Item

Explanation:

• Each pipeline value is bound to $Item.
• No prompting occurs because the pipeline supplies the values.

8. Why Mandatory Parameters Matter¶

Mandatory parameters ensure:

• The function always receives the data it needs
• Errors occur early, not halfway through execution
• Scripts behave predictably
• Users cannot accidentally run a function incorrectly

They are essential for building reliable, modular PowerShell code.