Detect missing filenames in folder - powershell

Question

Every day we receive a zipfile from a number of clients. The filename consists of the following:
data_clientname_timestamp.zip
Where "data" is always the same text, "clientname" could be anything and "timestamp" is the file creation date.
The files are always in the same directory. The clientnames are always known in advance, so I know what files should be received.
The script should do the following:
List all files received (created) today
If a file from one or more clients is missing, write "file from client.. missing" to a file
I would like to list the clients in a variable, so those can easily be changed.
What I have so far:
$folder='C:\data'
Get-ChildItem $folder -recurse -include #("*.zip") |
Where-Object {($_.CreationTime -gt (Get-Date).Date )} | select name | out-file $folder\result.txt
But how to check the file for missing files?
Edit:
Testdata:
$Timestamp = (Get-Date).tostring(“yyyyMMddhhmmss”)
New-Item c:\Data -type Directory
New-Item c:\Data\Data_client1_$Timestamp.zip -type file
New-Item c:\Data\Data_client2_$Timestamp.zip -type file
New-Item c:\Data\Data_client3_$Timestamp.zip -type file
New-Item c:\Data\Data_client5_$Timestamp.zip -type file
New-Item c:\Data\Data_client6_$Timestamp.zip -type file
New-Item c:\Data\Data_client7_$Timestamp.zip -type file
exit
Script:
$folder='C:\Data'
$clients = #("client1", "client2", "client3", "client4", "client5", "client6", "client7")
$files = Get-ChildItem $folder -recurse -include #("*.zip") |
Where-Object {($_.CreationTime -gt (Get-Date).Date )}
$files | Select-Object Name | Out-File $folder\result.txt
$files | Where-Object { ($_.Name -replace '.+?_([^_]+).*', '$1') -notin $clients} | Out-File $folder\result2.txt

Answer 1

Start with defining a list of clients you would expect like:
$clients = #("client1", "client2")
Then retrieve all zip files and save it to a variable:
$files = Get-ChildItem $folder -recurse -include #("*.zip") |
Where-Object {($_.CreationTime -gt (Get-Date).Date )}
Export the existing files to your result.txt:
$files | Select-Object Name | Out-File $folder\result.txt
Now you can determine each missing client using the Where-Object cmdlet with a regex that grabs the clientname:
$fileClients = $files | ForEach-Object { ($_.Name -replace '.+?_([^_]+).*', '$1') }
Compare-Object $clients $fileClients | select -ExpandProperty InputObject | Out-File $folder\result2.txt

Answer 2

You need to have a list of your clients somewhere (such as in a CSV file named clients.csv) then you could loop through that list to check if a file is found for each client. For example:
$folder='C:\data'
$Clients = Import-CSV Clients.csv
$Files = Get-ChildItem $folder -recurse -include #("*.zip") | Where-Object {($_.CreationTime -gt (Get-Date).Date )} | select name
$Clients | ForEach-Object {
$Client = $_
$ClientCheck = $Files | Where-Object {$_ -like $Client}
If (-not $ClientCheck) {
Write-Warning "$Client is missing!"
}Else{
Write-Output $ClientCheck
}
} | out-file $folder\result.txt