Techniques for PowerShell Parameters
On this page I want to show you methods for researching PowerShell parameters.
- Exploit a Cmdlet’s Help File
- Find Cmdlets that Use a Particular Parameter
- List Positional PowerShell Parameters
- PowerShell Declaring Function Parameters
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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
Clear-Host
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
Clear-Host
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
Clear-Host
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
Clear-Host
$a = Get-Command New*
Foreach ($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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