Pipeline processing

Another way that functions in PowerShell are different from other languages is how they interact with the pipeline. Functions in PowerShell output objects that can be picked up as input to subsequent functions or cmdlets. This in and of itself is not unique, but the timing of the output is different from other languages.

Consider the process of obtaining a listing of all of the files on a drive. For some drives this operation will be very lengthy, possibly taking several minutes to complete. In PowerShell though, the list of files begin to appear almost instantly. The process can take a while to be complete, but the function (Get-ChildItem) will output file and folder objects as each directory is scanned rather than waiting to have all of them collected in a list and returning the list all at once. This feature of built-in cmdlets is something that might easily be taken for granted, but when writing functions, the concept of a return value needs to be carefully considered...