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about_Splatting

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Short description

Describes how to use splatting to pass parameters to commands in PowerShell.

Long description

Splatting is a method of passing a collection of parameter values to a command as a unit. PowerShell associates each value in the collection with a command parameter. Splatted parameter values are stored in named splatting variables, which look like standard variables, but begin with an At symbol (@) instead of a dollar sign ($). The At symbol tells PowerShell that you are passing a collection of values, instead of a single value.

Splatting makes your commands shorter and easier to read. You can reuse the splatting values in different command calls and use splatting to pass parameter values from the $PSBoundParameters automatic variable to other scripts and functions.

Beginning in Windows PowerShell 3.0, you can also use splatting to represent all parameters of a command.

Syntax

<CommandName> <optional parameters> @<HashTable> <optional parameters>
<CommandName> <optional parameters> @<Array> <optional parameters>

To provide parameter values for positional parameters, in which parameter names are not required, use the array syntax. To provide parameter name and value pairs, use the hash table syntax. The splatted value can appear anywhere in the parameter list.

When splatting, you do not need to use a hash table or an array to pass all parameters. You may pass some parameters by using splatting and pass others by position or by parameter name. Also, you can splat multiple objects in a single command so you don't pass more than one value for each parameter.

As of PowerShell 7.1, you can override a splatted parameter by explicitly defining a parameter in a command.

Splatting with hash tables

Use a hash table to splat parameter name and value pairs. You can use this format for all parameter types, including positional and switch parameters. Positional parameters must be assigned by name.

The following examples compare two Copy-Item commands that copy the Test.txt file to the Test2.txt file in the same directory.

The first example uses the traditional format in which parameter names are included.

Copy-Item -Path "test.txt" -Destination "test2.txt" -WhatIf

The second example uses hash table splatting. The first command creates a hash table of parameter-name and parameter-value pairs and stores it in the $HashArguments variable. The second command uses the $HashArguments variable in a command with splatting. The At symbol (@HashArguments) replaces the dollar sign ($HashArguments) in the command.

To provide a value for the WhatIf switch parameter, use $True or $False.

$HashArguments = @{
  Path = "test.txt"
  Destination = "test2.txt"
  WhatIf = $true
}
Copy-Item @HashArguments

Note

In the first command, the At symbol (@) indicates a hash table, not a splatted value. The syntax for hash tables in PowerShell is: @{<name>=<value>; <name>=<value>; ...}

Splatting with arrays

Use an array to splat values for positional parameters, which do not require parameter names. The values must be in position-number order in the array.

The following examples compare two Copy-Item commands that copy the Test.txt file to the Test2.txt file in the same directory.

The first example uses the traditional format in which parameter names are omitted. The parameter values appear in position order in the command.

Copy-Item "test.txt" "test2.txt" -WhatIf

The second example uses array splatting. The first command creates an array of the parameter values and stores it in the $ArrayArguments variable. The values are in position order in the array. The second command uses the $ArrayArguments variable in a command in splatting. The At symbol (@ArrayArguments) replaces the dollar sign ($ArrayArguments) in the command.

$ArrayArguments = "test.txt", "test2.txt"
Copy-Item @ArrayArguments -WhatIf

Using the ArgumentList parameter

Several cmdlets have an ArgumentList parameter that is used to pass parameter values to a script block that is executed by the cmdlet. The ArgumentList parameter takes an array of values that is passed to the script block. PowerShell is effectively using array splatting to bind the values to the parameters of the script block. When using ArgumentList, if you need to pass an array as a single object bound to a single parameter, you must wrap the array as the only element of another array.

The following example has a script block that takes a single parameter that is an array of strings.

$array = 'Hello', 'World!'
Invoke-Command -ScriptBlock {
  param([string[]]$words) $words -join ' '
  } -ArgumentList $array

In this example, only the first item in $array is passed to the script block.

Hello

$array = 'Hello', 'World!'
Invoke-Command -ScriptBlock {
  param([string[]]$words) $words -join ' '
} -ArgumentList (,$array)

In this example, $array is wrapped in an array so that the entire array is passed to the script block as a single object.

Hello World!

Examples

Example 1: Reuse splatted parameters in different commands

This example shows how to reuse splatted values in different commands. The commands in this example use the Write-Host cmdlet to write messages to the host program console. It uses splatting to specify the foreground and background colors.

To change the colors of all commands, just change the value of the $Colors variable.

The first command creates a hash table of parameter names and values and stores the hash table in the $Colors variable.

$Colors = @{ForegroundColor = "black"; BackgroundColor = "white"}

The second and third commands use the $Colors variable for splatting in a Write-Host command. To use the $Colors variable, replace the dollar sign ($Colors) with an At symbol (@Colors).

#Write a message with the colors in $Colors
Write-Host "This is a test." @Colors

#Write second message with same colors. The position of splatted
#hash table does not matter.
Write-Host @Colors "This is another test."

Example 2: Forward parameters using $PSBoundParameters

This example shows how to forward their parameters to other commands by using splatting and the $PSBoundParameters automatic variable.

The $PSBoundParameters automatic variable is a dictionary object (System.Collections.Generic.Dictionary) that contains all the parameter names and values that are used when a script or function is run.

In the following example, we use the $PSBoundParameters variable to forward the parameters values passed to a script or function from Test2 function to the Test1 function. Both calls to the Test1 function from Test2 use splatting.

function Test1
{
    param($a, $b, $c)

    $a
    $b
    $c
}

function Test2
{
    param($a, $b, $c)

    #Call the Test1 function with $a, $b, and $c.
    Test1 @PsBoundParameters

    #Call the Test1 function with $b and $c, but not with $a
    $LimitedParameters = $PSBoundParameters
    $LimitedParameters.Remove("a") | Out-Null
    Test1 @LimitedParameters
}

Test2 -a 1 -b 2 -c 3
1
2
3
2
3

Example 3: Override splatted parameters with explicitly defined parameters

This example shows how to override a splatted parameter using explicitly defined parameters. This is useful when you don't want to build a new hashtable or change a value in the hashtable you are using to splat.

The $commonParams variable stores the parameters to create virtual machines in the East US location. The $allVms variable is a list of virtual machines to create. We loop through the list and use $commonParams to splat the parameters to create each virtual machine. However, we want myVM2 to be created in a different region than the other virtual machines. Instead of adjusting the $commonParams hashtable, you can explicitly define the Location parameter in New-AzVm to supersede the value of the Location key in $commonParams.

$commonParams = @{
    ResourceGroupName = "myResourceGroup"
    Location = "East US"
    VirtualNetworkName = "myVnet"
    SubnetName = "mySubnet"
    SecurityGroupName = "myNetworkSecurityGroup"
    PublicIpAddressName = "myPublicIpAddress"
}

$allVms = @('myVM1','myVM2','myVM3',)

foreach ($vm in $allVms)
{
    if ($vm -eq 'myVM2')
    {
        New-AzVm @commonParams -Name $vm -Location "West US"
    }
    else
    {
        New-AzVm @commonParams -Name $vm
    }
}

Splatting command parameters

You can use splatting to represent the parameters of a command. This technique is useful when you are creating a proxy function, that is, a function that calls another command. This feature is introduced in Windows PowerShell 3.0.

To splat the parameters of a command, use @Args to represent the command parameters. This technique is easier than enumerating command parameters and it works without revision even if the parameters of the called command change.

The feature uses the $Args automatic variable, which contains all unassigned parameter values.

For example, the following function calls the Get-Process cmdlet. In this function, @Args represents all the parameters of the Get-Process cmdlet.

function Get-MyProcess { Get-Process @Args }

When you use the Get-MyProcess function, all unassigned parameters and parameter values are passed to @Args, as shown in the following commands.

Get-MyProcess -Name PowerShell

Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)     Id ProcessName
-------  ------    -----      ----- -----   ------     -- -----------
    463      46   225484     237196   719    15.86   3228 powershell

Get-MyProcess -Name PowerShell_Ise -FileVersionInfo

ProductVersion   FileVersion      FileName
--------------   -----------      --------
6.2.9200.16384   6.2.9200.1638... C:\Windows\system32\WindowsPowerShell\...

You can use @Args in a function that has explicitly declared parameters. You can use it more than once in a function, but all parameters that you enter are passed to all instances of @Args, as shown in the following example.

function Get-MyCommand
{
    Param ([switch]$P, [switch]$C)
    if ($P) { Get-Process @Args }
    if ($C) { Get-Command @Args }
}

Get-MyCommand -P -C -Name PowerShell

Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)     Id ProcessName
-------  ------    -----      ----- -----   ------     -- -----------
408      28    75568      83176   620     1.33   1692 powershell

Path               : C:\Windows\System32\WindowsPowerShell\v1.0\powershell.e
Extension          : .exe
Definition         : C:\Windows\System32\WindowsPowerShell\v1.0\powershell.e
Visibility         : Public
OutputType         : {System.String}
Name               : powershell.exe
CommandType        : Application
ModuleName         :
Module             :
RemotingCapability : PowerShell
Parameters         :
ParameterSets      :
HelpUri            :
FileVersionInfo    : File:             C:\Windows\System32\WindowsPowerShell
                     \v1.0\powershell.exe
                     InternalName:     POWERSHELL
                     OriginalFilename: PowerShell.EXE.MUI
                     FileVersion:      10.0.14393.0 (rs1_release.160715-1616
                     FileDescription:  Windows PowerShell
                     Product:          Microsoft Windows Operating System
                     ProductVersion:   10.0.14393.0
                     Debug:            False
                     Patched:          False
                     PreRelease:       False
                     PrivateBuild:     False
                     SpecialBuild:     False
                     Language:         English (United States)

Notes

If you make a function into an advanced function by using either the CmdletBinding or Parameter attributes, the $args automatic variable is no longer available in the function. Advanced functions require explicit parameter definition.

PowerShell Desired State Configuration (DSC) was not designed to use splatting. You cannot use splatting to pass values into a DSC resource. For more information, see Gael Colas' article Pseudo-Splatting DSC Resources.

See also