Types of output handlers

Crescendo supports four types of output handlers.

  • ByPass
  • Inline
  • Function
  • Script

ByPass

When you set HandlerType to ByPass, the cmdlet does no output or error handling. Some command-line tools create different output depending on whether the output is sent to the screen or the pipeline. Pastel is an example of a command that changes its output from a graphical screen representation to a single string value when used in a pipeline. Crescendo output handling is pipeline based and can cause these applications to return unwanted results. Crescendo supports the ability to bypass the output handler entirely.

To bypass all output handling by Crescendo:

"OutputHandlers": [
    {
        "ParameterSetName": "Default",
        "HandlerType": "ByPass"
    }
]

Inline

This is the default HandlerType if you don’t specify the type. To use this type, set the Handler property to a string containing PowerShell code that handles the output. This is best suited for small handlers that easily fit into a single line. For example, you might have a command-line tool that can output JSON. You don’t need a complicated parsing function to convert the JSON to an object. The output from the ifconfig command in Linux can be transformed to JSON using jc. The JSON is easily converted to a PowerShell object using ConvertFrom-Json.

"OutputHandlers": [
    {
        "ParameterSetName": "Default",
        "HandlerType": "Inline",
        "StreamOutput": true,
        "Handler": "$input | jc --ifconfig | ConvertFrom-Json"
    }
]

Function

When you HandlerType to Function, the Handler property is the name of the function that parses the output. That function needs to be loaded in your PowerShell session before you run Export-CrescendoModule. Export-CrescendoModule copies the function into the module (.PSM1) file it creates.

This is the preferred way of including complex parsing functions.

Script

When you set HandlerType to Function, the Handler property is the name of the function that parses the output. The script file needs to in the current location relative to where you run Export-CrescendoModule. Export-CrescendoModule copies the script files into the module output location. These files need to be included with the module when you publish it.

This is useful for testing your module during development, because you don’t have to rebuild the module if you need to make changes to one of the output handler scripts.