Append an Array to an Array of Arrays in PowerShell

It’s a common gotcha, arrays (and other collections) may get unrolled “unexpectedly”. Use the comma operator (it makes/enforces an array with a single item and avoids unrolling):

$array1 = "11","12","13"
$array2 = "21","22","23"
$array3 = "31","32","33"

$arrayAll = $array1, $array2, $array3
$arrayAll.Count # returns 3

$arrayAll = @()
$arrayAll += , $array1
$arrayAll += , $array2
$arrayAll += , $array3

$arrayAll.count # returns 3

$arrayAll[1] # gets "21","22","23", i.e. $array2