PowerShell Parameter Techniques

Techniques for PowerShell Parameters

On this page I want to show you methods for researching PowerShell parameters.


Exploit a Cmdlet’s Help File

Each PowerShell cmdlet (or function) has it’s own help file, which is a rich source of parameter information.  Access could not easier, just precede the cmdlet with help.  However, there is one trick, always append -Full.  The benefit is that you get examples of the cmdlet and its parameters in action.

# PowerShell Parameter Help
Get-Help Get-WmiObject

Note 1: On its own, this instruction gives only the names of the parameters.

Much better to append -Full, and see how to use the parameters.

# PowerShell Parameter Help
Get-Help Get-WmiObject -Full

-Class <String>
Specifies the name of a WMI class. When this parameter is used, the cmdlet retrieves instances of the WMI class.

Required? true
Position? 1
Default value
Accept pipeline input? false
Accept wildcard characters? false

Note: Even Get-Help has help!  For instance researching Get-Help reveals that you could substitute -Detailed or -Examples for -Full.

Find Cmdlets that Use a Particular Parameter

Remoting is popular in PowerShell 2.0 and later, but which cmdlets support ComputerName?

# Find PowerShell Cmdlets with a ComputerName Parameter
Get-Command | Where-Object { $_.parameters.keys -Match "Computer"}

Note 2:  The key properties are revealed by: .parameters.keys.

Note 3: I prefer the match comparator, but you could try:
Where-Object { $_.parameters.keys -Contains "ComputerName"

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Named PowerShell Parameters

The more parameters that you employ in a PowerShell script, the greater the need to name them.

Take as an example, Get-Eventlog system,
This instruction works because even though ‘system’ is not a named parameter, it is in position 1, which is reserved for -LogName. 

Take another example, here we wish to truncate the log output by introducing -Newest 50; this parameter must be named as there are at least 3 parameters that could be in the second position.

# PowerShell Named Parameters
Get-EventLog system -Newest 50 -Message "*media*" -EntryType Error

List Positional PowerShell Parameters

Here is a trick script which makes use of ExpandedProperties to discover which cmdlets have positional parameters.

# PowerShell Position Parameter List
$a = Get-Command New*
Foreach ($cmdlet in $a) {
$Cmdlet.ParameterSets | Select-Object -ExpandProperty parameters | `
Where {$_.Position -gt "0" } | FT $Cmdlet.Name, Name, Position -auto

Note 4: This is a script to give you ideas for further research.  For example you broaden the search for cmdlets by changing the value of $a = Get-Command from New* to Get*.

Note 5: I also use a similar script to find Mandatory or Required parameters  See more on Mandatory PowerShell parameters »

Summary of PowerShell Parameter Introduction

The idea is that parameters modify a cmdlet, they can take it’s basic action and turn it to the outcome that you really want.  The best way to learn about these capabilities is to employ Get-Help to list a cmdlet’s parameters.

Time spend learning about parameters subtleties will make us better PowerShell scripters.

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See more Microsoft PowerShell tutorials

PowerShell Tutorials  • Methods  • Cmdlets  • PS Snapin  • Profile.ps1  • Exchange 2007

Command & Expression Mode  • PowerShell pipeline (|)  • PowerShell ‘where‘  • PowerShell ‘Sort’

Windows PowerShell Modules  • Import-Module  • PowerShell Module Directory 

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