Loop Confusion Comparing Objects - powershell

Question

I am trying to create my own service comparison script. I see some online but want to do this myself. I've only gotten so far. I keep getting confused.
The desired output is with the following format. It doesn't even have to show what's different. I just want to see what the previous state was compared to the current state. I did a compare-object and it didn't give me the format I desired. I then thought maybe I should just do two nested loops and create a new object with the states I want in it. It didn't work out correctly, it returns an array. So then I thought, maybe a for loop in the foreach loop... I keep confusing myself and it's so close.
You have to provide a csv with some services to compare to to make this work as part of it's paramaters.
Usage
Inspect-ServiceSnapshot -SnapshotPath "C:\YourPath"
Desired output
Name CurrentState PreviousState
app1 Running Stopped
Code So Far
function Inspect-ServiceSnapshot {
[CmdletBinding()]
param (
#Snapshot
[Parameter(Mandatory=$true)]
[ValidatePattern("C:")]
[string]
$SnapshotPath,
# timer
[Parameter(Mandatory=$false)]
[int]
$TimeToWait
)
if($TimeToWait -ne $null) {
Start-Sleep -Seconds $TimeToWait
$list = #()
$old = Import-Csv -Path $SnapshotPath
foreach($entry in (get-service)) {
foreach($oldItem in $old) {
$object = New-Object -TypeName psobject -Property #{
Name = $entry.Name
CurrentStatus = $entry.status
DisplayName = $entry.displayname
PreviousStatus = $oldItem.status
}
$list += $object
}
}
$list
} else {
$list = #()
$old = Import-Csv -Path $SnapshotPath
foreach($entry in (get-service)) {
foreach($oldItem in $old) {
$object = New-Object -TypeName psobject -Property #{
Name = $entry.Name
CurrentStatus = $entry.status
DisplayName = $entry.displayname
PreviousStatus = $oldItem.status
}
$list += $object
}
}
$list
}
}

Answer 1

This should do it because it is actually checking the value for the old service to be the same as the one Get-Service provides at a certain time.
function Inspect-ServiceSnapshot {
[CmdletBinding()]
param (
#Snapshot
[Parameter(Mandatory=$true)]
[ValidateScript({Test-Path $_ -PathType Leaf})]
[string]$SnapshotPath,
# timer
[Parameter(Mandatory=$false)]
[int]$TimeToWait = 0
)
if($TimeToWait) { Start-Sleep -Seconds $TimeToWait }
$list = #()
$old = Import-Csv -Path $SnapshotPath
foreach($entry in (Get-Service)) {
# make sure we are dealing with the SAME service
$oldItem = $old | Where-Object { $_.Name -eq $entry.Name }
$object = New-Object -TypeName psobject -Property #{
Name = $entry.Name
CurrentStatus = $entry.status
DisplayName = $entry.displayname
PreviousStatus = if ($oldItem) { $oldItem.status } else { 'Unknown' }
}
$list += $object
}
$list
}

Answer 2

This answer is assuming there are no new services added on a regular basis.
You almost got it! You can forgo the nested loops, get rid of the else block (it is redundant), and use an index loop. When you're using nested loops like that, you are iterating through all of the array elements in the $old array every time you iterate through one of the (get-service) objects. This can cause issues when your arrays include thousands of objects.
You can easily get to what you want by using a for loop.
e.g.
if($TimeToWait -ne $null) {
Start-Sleep -Seconds $TimeToWait
}
$list = #();
$old = Import-Csv -Path $SnapshotPath | Sort-Object Name;
$new = Get-Service | Sort-Object Name;
for ($i -eq 0; $i -lt $old.length -or $i -lt $new.length; $i++) {
$object = New-Object -TypeName psobject -Property #{
Name = $new[$i].Name
CurrentStatus = $new[$i].status
DisplayName = $new[$i].displayname
PreviousStatus = $old[$i].status
}
$list += $object;
}
$list;
A lot of your code is redundant and you can just do this all in one go. Since you're not technically comparing any objects, you can just populate the fields as they go.