The other day I was working on a Powershell function to return a list and filter it through a number of switch parameters; anyway if no switch is used I want to return a default, raw result without manipulation, in other words I want the result to look like this: One possible approach to obtain it is code similar to this: It works, but it’s not very elegant or efficient… for example, what if I need to add more switch options? I would have to add additional if statements but also update the last if to make sure no switch has been used. The example above can be refactored like this: The magic happens an line 17, here I have it on a one line but let me break it down: first, we can use Get-Command to retrieve the list of parameters for any script or function (here I have even getting the parameter list for the script ListSwitchParameters.ps1 from within the script itself) The Values property contains the list of ParameterNames, their type and a boolean indicating if the parameter is a SwitchParameter; since it’s switch parameters we’re looking for, it is easy to filter this list. Last, we…

I’ve been doing some more experiments with custom types after my previous post on this topic and when working with classes there is an additional consideration to keep in mind: depending on where the class is declared, the object type (actually, the type name) changes which in turn will affect how the custom format file needs to be crafted. For example, let’s consider an example where the type declaration is outside a function declaration: If we execute this function and check the output with Get-Member, the type name matches exactly the class name as expected: If, on the other hand I define the class as part of the function, things change: Now if I execute this function again and pipe the output to Get-Member, the type name returned uses the function name as a namespace declaration; this is important and must be taken into account and used in the view name if we want it to match and properly format the output for this custom type: One final note about OutputType: The OutputType attribute value is only a documentation note. It is not derived from the function code or compared to the actual function output. As such, the value might…

Now that I have my custom type I can use cmdlets such as Format-Table or Format-List to format its output while at the console, but it would be nice if I did not have to remember to usem the every time. Powershell uses Format.ps1xml to define how types should be formatted when their output is sent to the console and this technique can come to our rescue. If an output object exposes up to 4 properties, by default Powershell formats it as a table while objects with 5+ displayed properties are formatted as list for better readability; for example, in this first example I am selecting only four properties and Powershell prints data in a table format, while in the second example I am selecting five properties and Powershell presents then in a list: This is not always true though, for example Get-Process returns a table with 6 columns: This is because Get-Process returns a type that happens to have a custom format defined; which type is that? System.Diagnostic.Process. If we check $PSHOME and search the *.format.ps1xml files we can find that C:\Windows\System32\WindowsPowerShell\v1.0\DotNetTypes.format.ps1xml contains a definition for this .NET type: This is a relatively complex View definition with custom column…

Objects in Powershell do not necessarily have to have a defined type (or better, they can simply all be generic PSCustomObject) but from time to time it can be useful to use a custom type, for example to get nice TAB completion when passing those objects down the pipeline or to use custom formatting (more on this in a future post). Custom types are relatively easy to add; in essence, once we have an object ready to be returned as function output we can simply insert the type name in the TypeNames collection Here I am retrieving some properties from an Azure Sql Database, add them to a PSCustomObject and call $outObj.PSObject.TypeNames.Insert to insert a custom type name (AzSqlDatabaseSize) at index zero of the TypeNames collection. The output of commands would look like this: If I pipe the command to Get-Member instead, we can see the object type returned: Also, if I use this command in a pipeline I get TAB auto-completion: notice when I pipe the command to Where-Object (? is the shortcut) the property names suggested are exactly the ones returned by my custom type: Powershell 5 added classes support and custom types is one of the supported…

I spend a lot of time working at the Powershell console so it is common for me to type (or retype) the same command multiple times; of course I tend to not really retype the same command every time but rather use Get-History and related cmdlets to re-execute previous commands: The quickest way to re-execute a previous command is to use Invoke-History followed by the Id from Get-History: I like to use shortcuts (or aliases, as you can see from my history above 😊) so I would normally use h (Get-History) and r <id> (Invoke-History <id>). Sometimes I need to slightly modify the command before running it again, there’s an easy solution for that as well: Simply copy the CommandLine value from Get-History to the clipboard, paste it to the console and change what’s needed PSReadLine improves the history search capability, here’s a list of bound key handlers related to history management: For example, using Ctrl+R (search history backwards) I can type a part of a string (“keyhan” in this example) and PSReadLine shows the first matching command, I can either hit TAB to accept the command and run it, or use CTRL+R to cycle through other commands matching the…