Here is a very special (and very underdocumented) way to use PowerShell parameters. Have a look at this function:
#requires -Version 2 function Test-DollarUnderscore { param ( [Parameter(Mandatory=$true, ValueFromPipelineByPropertyName=$true)] [string] $Test ) process { "received: $Test" } }
It does not seem to be very unusual at first. You can assign values to the -Test parameter, and the function returns them:
PS C:\> Test-DollarUnderscore -Test 'Some Data' received: Some Data
But now check out what happens when you pipe data into the function:
PS C:\> 1..4 | Test-DollarUnderscore -Test { "I am receiving $_" }
received: I am receiving 1
received: I am receiving 2
received: I am receiving 3
received: I am receiving 4
The -Test parameter suddenly and automagically accepts script blocks (although the assigned type was a string), and inside of the script block, you have access to the incoming pipeline element.
You get this very special parameter support when you set ValueFromPipelineByPropertyName=$true with a mandatory paramater, and the incoming data has no property that matches the parameter.
Throughout this month, we'd like to point you to two awesome community-driven global PowerShell events taking place this year:
Europe: April 20-22: 3-day PowerShell Conference EU in Hannover, Germany, with more than 30+ speakers including Jeffrey Snover and Bruce Payette, and 60+ sessions (www.psconf.eu).
Asia: October 21-22: 2-day PowerShell Conference Asia in Singapore. Watch latest annoncements at www.psconf.asia
Both events have limited seats available so you may want to register early.
