foreach pipe in multipleline string - powershell

Question

Here is my code:
$collection1 = "1","2","3","4"
"
collection1:
$($collection1 | % {$_})
"
The output is:
collection1:
1 2 3 4
However, I'm expecting:
collection1:
1
2
3
4
So I changed my code to:
"
$($collection1 | % {$_ + "`n"})
"
Now, it shows:
collection1:
1
2
3
4
Why there is always an extra space in the front of each line?
Any way to remove them?
I tried to use Trim(), [String]::Format(), and few other ways, none is working as expected.

Answer 1

I think I found the answer... For anyone's interest...
$collection1 = "1","2","3","4"
$body = [System.Text.StringBuilder]::new()
foreach($item in $collection1)
{
[void]$body.Append($item+"`n")
}
"
collection1:
$body
"

Answer 2

$collection1 | % {$_} takes the array $collection1 and outputs each of its elements, which gives you the exact same thing you strated with: an array of the elements of $collection1. Using a subexpression to put that array into a string auto-converts the array to a string, so that it can be inserted into the outer string. In PowerShell this array-to-string conversion is done by joining the array elements with the $OFS character (Output Field Separator, by default a single space), which for your example produces the string "1 2 3 4".
The simplest way of getting the result you expect is to convert the array to a formatted string yourself:
"
collection1:
$($collection1 | Out-String)
"
The Out-String cmdlet converts array input to a single string by joining all input strings with newlines. Alternatively join the array yourself:
"
collection1:
$($collection1 -join "`n")
"
You could also (temporarily) modify $OFS and use the variable directly:
$OFS_bak = $OFS
$OFS = "`n"
"
collection1:
$collection1
"
$OFS = $OFS_bak
although I wouldn't normally recommend that.
As a side note: when working with a format/template string it's usually a good idea to use here-strings (so that don't need to escpae quotes inside the strings) and the format operator (-f):
#"
collection1:
{0}
"# -f ($collection1 | Out-String)