$files = Get-ChildItem -Filter "*instituts-formation-*"
foreach ($file in $files) {
    if ($file.Name -like "*regions.php") {
        Write-Host "Keeping index file: $($file.Name)"
        continue
    }
    $newName = $file.Name -replace "instituts-formation-", ""
    if (Test-Path $newName) {
        Write-Host "Short version already exists: $newName. Deleting long version: $($file.Name)"
        Remove-Item $file.FullName
    } else {
        Write-Host "Renaming $($file.Name) to $newName"
        Rename-Item -Path $file.FullName -NewName $newName
    }
}