Updating hash table values in a 'foreach' loop in PowerShell

Question

I\'m trying to loop through a hash table and set the value of each key to 5 and PowerShell gives an error:

$myHash = @{}
$myHash[\"a\"] = 1
$myHash[\"b\"] =          


        

Answer 1

Use clone:

foreach($key in ($myHash.clone()).keys){
    $myHash[$key] = 5
}

Or in the one-liner:

$myHash = ($myHash.clone()).keys | % {} {$myHash[$_] = 5} {$myHash}

Answer 2

There is a much simpler way of achieving this. You cannot change the value of a hashtable while enumerating it because of the fact that it's a reference type variable. It's exactly the same story in .NET.

Use the following syntax to get around it. We are converting the keys collection into a basic array using the @() notation. We make a copy of the keys collection, and reference that array instead which means we can now edit the hashtable.

$myHash = @{}
$myHash["a"] = 1
$myHash["b"] = 2
$myHash["c"] = 3

foreach($key in @($myHash.keys)){
    $myHash[$key] = 5
}

Answer 3

You do not need to clone the whole hashtable for this example. Just enumerating the key collection by forcing it to an array @(...) is enough:

foreach($key in @($myHash.keys)) {...

Answer 4

I'm new to PowerShell, but I'm quite a fan of using in-built functions, because I find it more readable. This is how I would tackle the problem, using GetEnumerator and Clone. This approach also allows one to reference to the existing hash values ($_.value) for modifying purposes.

$myHash = @{}
$myHash["a"] = 1 
$myHash["b"] = 2
$myHash["c"] = 3

$myHash.Clone().GetEnumerator() | foreach-object {$myHash.Set_Item($_.key, 5)}