Powershell - foreach loop is exiting prematurely? - powershell

Question

Forgive me, but I'm very new to Powershell. I'm having a problem understanding why my code is abruptly exiting the foreach loop once the code finds the book with an ID called "bk103". I'm expecting that the foreach loop iterate through the for loop 12 times since there are 12 books in the xml file. Why is it exiting early?
Thank you!
Set-Location 'C:\PowershellPractice\' #'
[int]$index = 0
[string] $xmlFilePath=’C:\PowershellPractice\books.xml’
[xml] $xmlContent = [xml] (Get-Content -Path $xmlFilePath)
$newSubNode = $xmlContent.CreateElement("security")
$newSubNode.SetAttribute("Mode", "transport")
$collection = $xmlContent.catalog.ChildNodes
Write-Host "Collection has " $collection.Count " elements in it!"
foreach ($item in $collection){
Write-Host "In foreach, index is " $index
if ($item.id -eq "bk103" -OR
$item.id -eq "bk105" -OR
$item.id -eq "bk108" -OR
$item.id -eq "bk109"){
Write-Host "Found book called " $ $item.id
$elementCopy = $xmlContent.catalog.book[$index].Clone()
$elementCopy.AppendChild($newSubNode)
$xmlContent.catalog.RemoveChild($item)
$xmlContent.catalog.InsertBefore($elementCopy,$xmlContent.catalog.book[$index])
}
$index++
}
$xmlContent.Save('C:\PowershellPractice\books-edited.xml')

Answer 1

As mentioned in the comments, you cannot modify the collection while you're currently iterating over it.
Since you only really need to modify the elements in the collections themselves, I would recommend just doing that (instead of cloning the book node and re-attaching it):
foreach ($item in $collection){
Write-Host "In foreach, index is " $index
if ($item.id -eq "bk103" -OR
$item.id -eq "bk105" -OR
$item.id -eq "bk108" -OR
$item.id -eq "bk109"){
# Add subnode to matching $item
[void]$item.AppendChild($newSubNode)
}
}
If you ever find yourself in a situation where you cannot modify the element in place, use two loops - one to find the interesting elements, and another one to replace them by iterating over the resulting subset:
# collect matching results
$foundbooks = foreach ($item in $collection){
Write-Host "In foreach, index is " $index
if ($item.id -eq "bk103" -OR
$item.id -eq "bk105" -OR
$item.id -eq "bk108" -OR
$item.id -eq "bk109"){
# return matching $item
$item
}
}
# now modify based on initial results
foreach($book in $foundbooks){
Write-Host "Found book called " $ $book.id
$elementCopy = $book.Clone()
[void]$elementCopy.AppendChild($newSubNode)
[void]$xmlContent.catalog.InsertBefore($elementCopy,$book)
[void]$xmlContent.catalog.RemoveChild($book)
}