Parameters

Correct Format for Parameter Block

An empty parameter block should be displayed on its own line like this: param ().
A non-empty parameter block should have the opening and closing parentheses on their own line.
All text inside the parameter block should be indented once.
Every parameter should include the [Parameter()] attribute, regardless of whether the attribute requires decoration or not.
A parameter that is mandatory should contain this decoration: [Parameter(Mandatory = $true)].
A parameter that is not mandatory should not contain a Mandatory decoration in the [Parameter()].

Bad:

function Write-Nothing
{
    param
    (

    )

    Write-Verbose -Message 'Nothing'
}

Bad:

function Write-Text
{
    param([Parameter(Mandatory = $true)]
[ValidateNotNullOrEmpty()]
                    [String] $Text )

    Write-Verbose -Message $Text
}

Bad:

function Write-Text
{
    param
    (
        [Parameter(Mandatory)]
        [ValidateNotNullOrEmpty()]
        [String]
        $Text

        [Parameter(Mandatory = $false)]
        [ValidateNotNullOrEmpty()]
        [String]
        $PrefixText

        [Boolean]
        $AsWarning = $false
    )

    if ($AsWarning)
    {
        Write-Warning -Message "$PrefixText - $Text"
    }
    else
    {
        Write-Verbose -Message "$PrefixText - $Text"
    }
}

Good:

function Write-Nothing
{
    param ()

    Write-Verbose -Message 'Nothing'
}

Good:

function Write-Text
{
    param
    (
        [Parameter(Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [String]
        $Text
    )

    Write-Verbose -Message $Text
}

Good:

function Write-Text
{
    param
    (
        [Parameter(Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [String]
        $Text

        [Parameter()]
        [ValidateNotNullOrEmpty()]
        [String]
        $PrefixText

        [Parameter()]
        [Boolean]
        $AsWarning = $false
    )

    if ($AsWarning)
    {
        Write-Warning -Message "$PrefixText - $Text"
    }
    else
    {
        Write-Verbose -Message "$PrefixText - $Text"
    }
}

Parameter Names Use Pascal Case

All parameters must use PascalCase. This means that each concatenated word is capitalized.

Bad:

function Get-TargetResource
{
    [CmdletBinding()]
    param
    (
        $SOURCEPATH
    )
}

Bad:

function Get-TargetResource
{
    [CmdletBinding()]
    param
    (
        $sourcepath
    )
}

Good:

function Get-TargetResource
{
    [CmdletBinding()]
    param
    (
        [Parameter()]
        $SourcePath
    )
}

Parameters Separated by One Line

Parameters must be separated by a single, blank line.

Bad:

function New-Event
{
    param
    (
        [Parameter(Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [String]
        $Message,
        [ValidateSet('operational', 'debug', 'analytic')]
        [String]
        $Channel = 'operational'
    )
}

Good:

function New-Event
{
    param
    (
        [Parameter(Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [String]
        $Message,

        [Parameter()]
        [ValidateSet('operational', 'debug', 'analytic')]
        [String]
        $Channel = 'operational'
    )
}

Parameter Type on Line Above

The parameter type must be on its own line above the parameter name. If an attribute needs to follow the type, it should also have its own line between the parameter type and the parameter name.

Bad:

function Get-TargetResource
{
    [CmdletBinding()]
    param
    (
        [String] $SourcePath = 'c:\'
    )
}

Good:

function Get-TargetResource
{
    [CmdletBinding()]
    param
    (
        [Parameter()]
        [String]
        $SourcePath = 'c:\'
    )
}

Good:

function Get-TargetResource
{
    [CmdletBinding()]
    param
    (
        [Parameter()]
        [PSCredential]
        [Credential()]
        $MyCredential
    )
}

Good:

function New-Event
{
    param
    (
        [Parameter(Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [String]
        $Message,

        [Parameter()]
        [ValidateSet('operational', 'debug', 'analytic')]
        [String]
        $Channel = 'operational'
    )
}

Parameter Attributes on Separate Lines

Parameter attributes should each have their own line. All attributes should go above the parameter type, except those that must be between the type and the name.

Bad:

function New-Event
{
    param
    (
        [Parameter(Mandatory = $true)][ValidateNotNullOrEmpty()][String]
        $Message,

        [ValidateSet('operational', 'debug', 'analytic')][String]
        $Channel = 'operational'
    )
}

Good:

function New-Event
{
    param
    (
        [Parameter(Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [String]
        $Message,

        [Parameter()]
        [ValidateSet('operational', 'debug', 'analytic')]
        [String]
        $Channel = 'operational'
    )
}

Updated on 28 Jan 2019