What is the difference between a cmdlet and a function?

There are two elements in a module manifest: cmdlet and function.

What is the difference between a cmdlet and a function?

2 Answers
2

A cmdlet is a .NET class written in C# or other .NET language and contained in a .dll (i.e. in a binary module). A function is specified directly in PowerShell in a script, script module or at the command line. A module manifest may include both script and binary modules so the manifest needs to be able to export both cmdlets and functions. It's even possible to have both a cmdlet and a function with the same name exported from a single manifest though that's generally not recommended.

To complement Bruce Payette's helpful answer:

Not all functions are created equal in PowerShell:

An advanced function is the written-in-PowerShell analog of a cmdlet (which, as stated, is compiled from a .NET language); decorating a function's param(...) block with the [CmdletBinding()] attribute or decorating at least one parameter with a [Parameter()] attribute ^{thanks, Ansgar Wiechers}
is what makes it an advanced one; as such, it supports certain standard behaviors:

param(...)

[CmdletBinding()]

[Parameter()]

-Verbose

-OutVariable

-WhatIf

-Confirm

Typically, but not necessarily, advanced functions support one-by-one pipeline-input processing via a process ... script block, via parameter-binding parameters decorated with ValueFromPipeline and/or ValueFromPipelineByPropertyName.

process ...

ValueFromPipeline

ValueFromPipelineByPropertyName

Unfortunately, even advanced functions and cmdlets aren't created fully equal:

ValueFromRemainingAguments

A simple function, by contrast:

$Input

process ...

Filter

$_

While exporting functions as as part of a module - preferably via its module manifest (*.psd1) - doesn't enforce that functions be advanced ones, it is good practice to only exported advanced functions.

*.psd1

SupportsShouldProcess=$true

SupportsShouldProcess=$false

SupportsShouldProcess

-WhatIf

-Confirm

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