What is the difference between dot (.) and ampersand (&) in PowerShell?

Question

In PowerShell, what is the difference between using dot (.) and ampersand (&) when invoking a cmdlet, function, script file, or operable program?

Answer 1

You can also run things inside a module scope with the call operator, from my notes from Windows Powershell in Action.

# get and variable in module scope
$m = get-module counter
& $m Get-Variable count
& $m Set-Variable count 33

# see func def
& $m Get-Item function:Get-Count

# redefine func in memory
& $m {
  function script:Get-Count
  {
    return $script:count += $increment * 2
  }
}

# get original func def on disk
Import-Module .\counter.psm1 -Force

A few other things:

# run with commandinfo object
$d = get-command get-date
& $d

# call anonymous function
& {param($x,$y) $x+$y} 2 5

# same with dot operator
. {param($x,$y) $x+$y} 2 5