In Powershell, what is $input for? [duplicate]

Question

I was trying to create a hash table,

$input = @{'G'=100;'E'=50;'D'=35;'A'=100}

and could not figure out for the life of me why it wouldn't display as usual with commands like write-host, or simply $input. write-host returned System.Collections.ArrayList+ArrayListEnumeratorSimple. $input returned nothing. No error was thrown.

On a hunch I renamed the hash table, and boom, it appears as normal. Opening a new powershell tab in ISE, I observe that the variable $input is filled in with intellisense even though I have not defined it in this environment.

Now I'm curious: what is this system variable $input for? I'm on version 4.

Answer 1

It's an automatic variable:

$INPUT

Contains an enumerator that enumerates all input that is passed to a function. The $input variable is available only to functions and script blocks (which are unnamed functions). In the Process block of a function, the $input variable enumerates the object that is currently in the pipeline. When the Process block completes, there are no objects left in the pipeline, so the $input variable enumerates an empty collection. If the function does not have a Process block, then in the End block, the $input variable enumerates the collection of all input to the function.

This is also available in PowerShell:

Get-Help about_Automatic_Variables

I also have an open feature request for Set-StrictMode to handle detection of this.