Regex Get a substring from a string nearest to the end - regex

Question

I'm trying to get a substring from a string using a powershell script and regex.
For example I'm trying to get a year that's part of a filename.
Example Filename "Expo.2000.Brazilian.Pavillon.after.Something.2016.SomeTextIDontNeed.jpg"
The problem is that the result of the regex gives me "2000" and no other matches. I need to get "2016" matched. Sadly $matches only has one matched instance. Do I have missed something? I feel getting nuts ;)
If $matches would contain all instances found I could handle getting the nearest to end instance with:
$Year = $matches[$matches.Count-1]
Powershell Code:
# Function to get the images year and clean up image information after it.
Function Remove-String-Behind-Year
{
param
(
[string]$OriginalFileName # Provide the BaseName of the image file.
)
[Regex]$RegExYear = [Regex]"(?<=\.)\d{4}(?=\.|$)" Regex to match a four digit string, prepended by a dot and followed by a dot or the end of the string.
$OriginalFileName -match $RegExYear # Matches the Original Filename with the Regex
Write-Host "Count: " $matches.Count # Why I only get 1 result?
Write-Host "BLA: " $matches[0] # First and only match is "2000"
}
Wanted Result Table:
"x.2000.y.2016.z" => "2016" (Does not work)
"x.y.2016" => "2016" (Works)
"x.y.2016.z" => "2016" (Works)
"x.y.20164.z" => "" (Works)
"x.y.201.z" => "" (Works)

Answer 1

PowerShell's -match operator only ever finds (at most) one match (although multiple substrings of that one match may be found with capture groups).
However, using the fact that quantifier * is greedy (by default), we can still use that one match to find the last match in the input:
-match '^.*\.(\d{4})\b' finds the longest prefix of the input that ends in a 4-digit sequence preceded by a literal . and followed by a word boundary, so that $matches[1] then contains the last occurrence of such a 4-digit sequence.
Function Extract-Year
{
param
(
[string] $OriginalFileName # Provide the BaseName of the image file.
)
if ($OriginalFileName -match '^.*\.(\d{4})\b') {
$matches[1] # output last 4-digit sequence found
} else {
'' # output empty string to indicate that no 4-digit sequence was found.
}
}
'x.2000.y.2016.z', 'x.y.2016', 'x.y.2016.z', 'x.y.20164.z', 'x.y.201.z' |
% { Extract-Year $_ }
yields
2016
2016
2016
# empty line
# empty line