What the unary comma does

While reading Powershell in Action, I got stuck on a passage in Chapter 5. I follow the result here, but could someone explain the purpose and the reason behind it?

$nested = 4, (5, 6)
$flattened = $nested | foreach { $_ }

$flattened.length

That gives $flattened.length as 3. Fair enough.

$nested = 4, (5, 6)
$flattened = $nested | foreach { ,$_ }

$flattened.length

This time $flattened.length gives 2.

Running $flattened[0]; $flattened[1] -join "," explains those 2 objects, but what precisely does the comma inside that second ForEach accomplish?

Does it mean, roughly, “Keep 4 as an object and (5,6) as its seperate object. Leave them intact.”

The conversation continues 3

Follow the reasoning

Nadia23 Sept Permalink
The Powershell pipeline “unwraps” collections for convenience and, amusingly, for user “consistency”. That unary operator stops powershell from performing that unwrapping. Those examples aren't ideal, so I'll try another approach.

Look at what these two snippets produce
```
(4, 5, 6) | ForEach-Object {
    Write-Host "Pipeline element now: $_"
}

Pipeline element now: 4
Pipeline element now: 5
Pipeline element now: 6
```
```
,(4, 5, 6) | ForEach-Object {
    Write-Host "Pipeline element now: $_"
}

Pipeline element now: 4 5 6
```
The latter sends the complete collection through as a single object, so it never gets unwrapped. It's an array, and the spaces you see, rather than commas, come from the space used as the default output field separator (held in $ofs). Here's a way to observe that
```
"$(4, 5, 6)"

4 5 6
```
Embedding that array in a string makes powershell join its elements using the default OFS. Changing it is possible, although seldom necessary.
```
$ofs = '/~/'

"$(4, 5, 6)"

4/~/5/~/6
```
One fairly frequent use for that unary operator in my own work is splitting values while keeping every element together in a single object.
```
,(-split 'Tavin enjoys powershell') | ForEach-Object {
    [PSCustomObject]@{
        Who   = $_[0]
        Does  = $_[1]
        Topic = $_[2]
    }
}

Who   Does   Topic
---   ----   -----
Tavin enjoys powershell
```
e.marsh23 Sept Permalink
Following an earlier reply ↗
Thanks! That makes it FAR clearer now. Particularly trying that final example with the unary operator removed.

I just couldn't get comfortable with the example from the book.
snip9 Oct Permalink
Following an earlier reply ↗
Much obliged for posting this, kind sir. Many thanks.

What the unary comma does

The conversation continues 3

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