Passing Boolean values to Powershell modules

Often times we need to pass a Boolean value to a Powershell provider, and a perfect example is for the purpose of a “debug” flag.

In my experience, Powershell probe and write action modules always type cast the script input parameter as String, whether the configuration element is of type Boolean or String. This means the default value in your workflow could be true, false, 1, or 0, and it will always equal true if you are handling this input parameter as Boolean in the script.

Obviously, this will cause some unexpected behaviors, and most likely will be viewed as a bug in the management pack.

The way I work around this issue (at least until this is fixed in the product) is NOT typing the script parameter, and then converting the variable to Boolean just after the param block like this:

$debugFlag = [System.Convert]::ToBoolean($debugFlag)

By handling a Boolean input parameter like this in the script, we can effectively use the Boolean type in module configuration; the default value in the monitoring workflow can be true or false, the value will be handled appropriately by the script, the operator will see the default value as it should appear in console, and the operator will be presented with a meaningful (True|False) selector in the override interface.

UPDATE (09/02/2015) – This problem applies to Boolean, Integer, and Double values!

After writing this post, I wanted to get down to the bottom of the problem, so I poked around the Windows Library and what I found made it clear.

Taking a look at the implementation of any Powershell probe module, you will notice the Parameters element type is NamedParametersType, and this is defined in the Microsoft.Windows.PowerShellSchema. Notice the name-value pair are of type ID and string, respectively. This is the reason any type of value will be cast as String in a Powershell module.

<SchemaType ID="Microsoft.Windows.PowerShellSchema" Accessibility="Public"> 
<xsd:complexType name="NamedParametersType">
<xsd:element name="Parameter" minOccurs="0" maxOccurs="unbounded">
<xsd:element name="Name" type="xsd:ID" />
<xsd:element name="Value" type="xsd:string" />
<xsd:complexType name="SnapInsType">
<xsd:element name="SnapIn" minOccurs="0" maxOccurs="unbounded" type="xsd:string" />
<xsd:simpleType name="NonNullString">
<xsd:restriction base="xsd:string">
<xsd:minLength value="1" />

It seems to me, the way to resolve this is to update the library with a choice for value type. This would allow the developer the option to type cast, and would remove the assumption that type casting is occurring when it is not. Since this schema exists in the Microsoft Windows Library, it would make the most sense for Microsoft to fix this.

One thought on “Passing Boolean values to Powershell modules”

  1. You could also use the default string method .ToBoolean. E.g. ‘true’.ToBoolean($_)

    In your example:
    $debugFlag = $debugFlag.ToBoolean($_)

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