{"id":4522,"date":"2012-12-03T00:01:00","date_gmt":"2012-12-03T00:01:00","guid":{"rendered":"https:\/\/blogs.technet.microsoft.com\/heyscriptingguy\/2012\/12\/03\/use-powershell-default-parameter-values-to-simplify-scripts\/"},"modified":"2012-12-03T00:01:00","modified_gmt":"2012-12-03T00:01:00","slug":"use-powershell-default-parameter-values-to-simplify-scripts","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/scripting\/use-powershell-default-parameter-values-to-simplify-scripts\/","title":{"rendered":"Use PowerShell Default Parameter Values to Simplify Scripts"},"content":{"rendered":"

Summary:<\/strong> Microsoft PowerShell MVP and guest blogger Dave Moravec talks about using default parameter values to simplify Windows PowerShell scripts.<\/p>\n

Microsoft Scripting Guy, Ed Wilson, is here. Well, our European Tour is drawing down, but it’s not over yet. Yesterday, we had a great time with Bartek in Warsaw, and last night we took the train back from Warsaw to Berlin.<\/p>\n

This morning, we are on a train to Prague to see Windows PowerShell MVP Dave Moravec. We will not have too much time—only about six hours before we have to hop back on a train to Frankfurt. But when Dave began talking to the Scripting Wife on Facebook and on Twitter, well, it was decided that we had the time, and we wanted to meet Dave. In honor of the occasion, I asked Dave to write a little bit about his favorite Windows PowerShell 3.0 feature. I will admit I was a bit surprised by his choice—perhaps you will be as well.<\/p>\n

Take it away, Dave …<\/p>\n

I have been in the IT industry for 15 years. The last 10 years working mainly with Microsoft management technologies. I work for one of the biggest international accounting companies as an administrator responsible for System Center: Configuration Manager (SCCM). I like to automate my infrastructure-related tasks with Windows PowerShell. I’m an author and speaker for Microsoft Czech Republic, and I run my own blog at PowerShell.cz<\/a>. You can reach me on Twitter at @makovec<\/a>.<\/p>\n

Changing default parameter values<\/h2>\n

When I was asked to write about my favorite Windows PowerShell 3.0 feature, my #1 $PSDefaultParameterValues<\/strong> came to mind immediately. From my point of view, this was something I was looking for, for a long time.<\/p>\n

How does it work? With $PSDefaultParameterValues<\/strong>, you can define (overwrite) default values of parameters for Windows PowerShell cmdlets. Actually, I just found that Scripting Guy already showed a nice usage of this a month ago in his PowerTip: Automatically Format Your PowerShell Table<\/a>. Let me show you a few other practical examples.<\/p>\n

How to set a default value<\/h2>\n

Let’s imagine you work frequently with Windows PowerShell jobs (and I am sure you do!). So I will use a really complicated example:<\/p>\n

  PS> Start-Job -Name sj -ScriptBlock { $pid } | Wait-Job | Receive-Job<\/p>\n

  8828<\/p>\n

  PS> Receive-Job -Name sj<\/p>\n

  PS><\/p>\n

No result received, as expected. If you want to leave the data in queue, you have to use the –Keep<\/strong> switch parameter. By using $PSDefaultParameterValues<\/strong>, you can tell PowerShell to set –Keep<\/strong> to True every time. $PSDefaultParameterValues<\/strong> is a hash table where the Key is combination of CmdletName:ParameterName<\/strong> and Value is the actual value you want to assign. In our example, the assignment is:<\/p>\n

 PS> $PSDefaultParameterValues = @{‘Receive-Job:Keep’=$true}<\/p>\n

You see that for the Keep<\/strong> parameter of the Receive-Job<\/strong> cmdlet, we used variable $true<\/strong> (as it is a switch, True means it’s enabled), so now we can write:<\/p>\n

  PS> Start-Job -Name sj2 -ScriptBlock { $pid } | Wait-Job | Receive-Job<\/p>\n

  2433<\/p>\n

  PS> Receive-Job -Name sj2<\/p>\n

  2432<\/p>\n

  PS><\/p>\n

If you check $PSDefaultParameterValues<\/strong>, you can see that it’s really a hash table.<\/p>\n

  PS> $PSDefaultParameterValues<\/p>\n

  Name                   Value<\/p>\n

  —-                   —–<\/p>\n

  Receive-Job:Keep       True<\/p>\n

If you want to overwrite the actual default value, you can specify $false<\/strong> for Keep<\/strong> parameter<\/p>\n

  PS> Start-Job -Name sj3 -ScriptBlock { $pid } | Wait-Job | Receive-Job –Keep:$false<\/p>\n

  998<\/p>\n

  PS> Receive-Job -Name sj3<\/p>\n

  PS><\/p>\n

Another usage for $PSDefaultParameterValues<\/strong> I found relates to work with the Export-Csv<\/strong> cmdlet. I export a lot of data from our infrastructure very often and pass them on in CSV format to my boss. Therefore, I don’t like the default behavior, which includes type info at the beginning of the file. I decided to change that. Furthermore, as work with different language settings, I also changed the delimiter.<\/p>\n

  PS> $PSDefaultParameterValues = @{‘Export-Csv:Delimiter’=’;’; ‘Export-Csv:NoTypeInformation’=$true}<\/p>\n

  PS> Get-Process -Name p* | Select Name, WS | Export-Csv -Path c:\\tmp\\ps.csv<\/p>\n

  PS> Get-Content C:\\tmp\\ps.csv<\/p>\n

  “Name”;”WS”<\/p>\n

  “powershell_ise”;”17477223’<\/p>\n

 <\/p>\n

  PS> $PSDefaultParameterValues<\/p>\n

  Name                            Value<\/p>\n

  —-                            —–<\/p>\n

  Export-Csv:Delimiter            ;<\/p>\n

  Export-Csv:NoTypeInformation    True<\/p>\n

Works like a charm, but in the last output, you may have noticed an unpleasant surprise. Our modification from the first example (Receive-Job<\/strong>) disappeared. You probably discovered it happened during our second modification of $PSDefaultParameterValues<\/strong>. To avoid this, we will use techniques for work with the hash tables. There are two different possibilities:<\/p>\n

  PS> $PSDefaultParameterValues[‘Receive-Job:Keep’]=$true<\/p>\n

  PS> $PSDefaultParameterValues.Add(‘Enter-PSSession:ComputerName’, ‘localhost’)<\/p>\n

After that, two additional default values were received, and we should have four in total now. Let’s check it:<\/p>\n

  PS> $PSDefaultParameterValues<\/p>\n

  Name                            Value<\/p>\n

  —-                            —–<\/p>\n

  Export-Csv:Delimiter            ;<\/p>\n

  Receive-Job:Keep                True<\/p>\n

  Export-Csv:NoTypeInformation    True<\/p>\n

  Enter-PSSession:ComputerName    localhost<\/p>\n

You can immediately test newly added values. As of now, if you write Enter-PSSession<\/strong>, you will be connected to your local computer by default. This is probably not so useful, so feel free to modify it for the server you are mostly connecting to.<\/p>\n

There are other options for $PSDefaultParameterValues<\/strong> modification:<\/p>\n