Parameters

Script Parameters / Arguments (for scripts, functions and script blocks)

Pass arguments to a script or cmdlet by separating them with spaces:

PS C:\> Get-ChildItem -Path $env:windir -Filter *.dll -Recurse

This can be made a little more readable by breaking up long lines with PowerShell’s escape character:
PS C:\> Get-ChildItem `
  -Path $env:windir `
  -Filter *.dll `
  -Recurse

To pass multiple arguments to a script you can splat them:

$myargs = @{
  Path = "$env:windir"
  filter = '*.dll
  Recurse = $true
}
Get-ChildItem @myargs

The above will be expanded to: Get-ChildItem -Path $env:windir -Filter *.dll -Recurse

Within a script or function you can refer to unnamed arguments using the $args array, for example passing all the arguments through to a cmdlet. You can also refer to specific arguments by their position:

"First argument is " + $Args[0]"
"Second argument is " + $Args[1]"

Param

To define arguments by name, use a param statement, which is simply a comma separated list of variables optionally with default values and data types:

param (
    [string]$price = 100, 
    [string]$ComputerName = $env:computername,    
    [string]$username = $(throw "-username is required."),
    [string]$password = $( Read-Host -asSecureString "Input password" )
    [switch]$SaveData = $false
)

write-output "First argument is $price"
write-output "Second argument is $ComputerName"
write-output "The True/False switch argument is $SaveData"

Calling this script, and setting the switch parameter -SaveData to $TRUE:
.\demo.ps1 -ComputerName "\\server64" -SaveData

or setting -SaveData to $FALSE:
.\demo.ps1 -ComputerName "\\server64" -SaveData:$false

In PowerShell 3.0 if an argument is omitted, there is an implied default value of $true

Cmdlet Parameters

Almost every PowerShell cmdlet can accept one or more optional parameters which can be supplied on the command line in the form -Parameter_Name Parameter_Value

The name of the parameter is always preceded by a hyphen (-)

The Parameter_value often needs to be provided in a specific data type (e.g. string or integer)
To find these details use Get-Help -detailed cmdletName

In some cases, the Parameter_Name is implied and does not need to be explicitly included.

In syntax descriptions:

 [-Param] -- is optional 
  -Param  -- is required

If you exclude the Parameter Names you must ensure that the Parameter Values are listed in the correct order (assuming more than one value is being passed .)

Parameter Names will be ignored if contained in quotation marks.

Multiple values (for the same parameter) can be separated with commas.

Parameters for external commands

When calling a non-PowerShell command or utility then the parameters won't follow any PowerShell conventions, see the & CALL operator page for full details, but generally any arguments to external commands should only be surrounded in quotes if needed due to spaces/long filenames, (just like the CMD shell).

CmdletBinding

An Advanced Function is one that contains the [cmdletbinding()] attribute. This adds several capabilities such as additional parameter checking, and the ability to easily use Write-Verbose.
A function with cmdletbinding will throw an error if unhandled parameter values appear on the command line.

“Slow down and enjoy life. It's not only the scenery you miss by going too fast, you also miss the sense of where you are going and why” - Eddie Cantor

Related:

& (call) - Run a command, script or function
Pipelines - Pass objects down the pipeline.
Wildcards - Match multiple items.


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