Merging hashtables in PowerShell: how?

Question

I am trying to merge two hashtables, overwriting key-value pairs in the first if the same key exists in the second.

To do this I wrote this function which first remo

Answer 1

In case you want to merge the whole hashtable tree

function Join-HashTableTree {
    param (
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [hashtable]
        $SourceHashtable,

        [Parameter(Mandatory = $true, Position = 0)]
        [hashtable]
        $JoinedHashtable
    )

    $output = $SourceHashtable.Clone()

    foreach ($key in $JoinedHashtable.Keys) {
        $oldValue = $output[$key]
        $newValue = $JoinedHashtable[$key]

        $output[$key] =
        if ($oldValue -is [hashtable] -and $newValue -is [hashtable]) { $oldValue | ~+ $newValue }
        elseif ($oldValue -is [array] -and $newValue -is [array]) { $oldValue + $newValue }
        else { $newValue }
    }

    $output;
}

Then, it can be used like this:

Set-Alias -Name '~+' -Value Join-HashTableTree -Option AllScope

@{
    a = 1;
    b = @{
        ba = 2;
        bb = 3
    };
    c = @{
        val = 'value1';
        arr = @(
            'Foo'
        )
    }
} |

~+ @{
    b = @{
        bb = 33;
        bc = 'hello'
    };
    c = @{
        arr = @(
            'Bar'
        )
    };
    d = @(
        42
    )
} |

ConvertTo-Json

It will produce the following output:

{
  "a": 1,
  "d": 42,
  "c": {
    "val": "value1",
    "arr": [
      "Foo",
      "Bar"
    ]
  },
  "b": {
    "bb": 33,
    "ba": 2,
    "bc": "hello"
  }
}