Download most recent file from FTP using PowerShell

Question

I am working on a PowerShell script, which will pull files from an FTP site. The files are uploaded to the FTP site every hour so I need to download the most recent one. The code I currently have downloads all the files from today instead of just one file. How do I make it download only the most recent file?

Here is the code that I am currently using

$ftpPath = 'ftp://***.***.*.*'
$ftpUser = '******'
$ftpPass = '******'
$localPath = 'C:\Temp'
$Date = get-date -Format "ddMMyyyy"
$Files = 'File1', 'File2'

function Get-FtpDir ($url, $credentials)
{
  $request = [Net.FtpWebRequest]::Create($url)
  if ($credentials) { $request.Credentials = $credentials }
  $request.Method = [System.Net.WebRequestMethods+FTP]::ListDirectory
  (New-Object IO.StreamReader $request.GetResponse().GetResponseStream()) -split "`r`n" 

}

$webclient = New-Object System.Net.WebClient 
$webclient.Credentials = New-Object System.Net.NetworkCredential($ftpUser,$ftpPass)  
$webclient.BaseAddress = $ftpPath

Foreach ( $item in $Files )
{
    Get-FTPDir $ftpPath $webclient.Credentials |
      ? { $_ -Like $item+$Date+'*' } |
      % {

          $webClient.DownloadFile($_, (Join-Path $localPath $_)) 
      }
}

Answer 1

It's not easy with the FtpWebRequest. For your task, you need to know file timestamps.

Unfortunately, there's no really reliable and efficient way to retrieve timestamps using features offered by FtpWebRequest/.NET framework/PowerShell as they do not support an FTP MLSD command. The MLSD command provides listing of remote directory in a standardized machine-readable format. The command and the format is standardized by RFC 3659.

Alternatives which you can use, that are supported by .NET framework:

• ListDirectoryDetails method (an FTP LIST command) to retrieve details of all files in a directory and then you deal with FTP server specific format of the details (*nix format similar to ls *nix command is the most common, drawback is that the format may change over time, as for newer files "May 8 17:48" format is used and for older files "Oct 18 2009" format is used)
• GetDateTimestamp method (an FTP MDTM command) to individually retrieve timestamps for each file. Advantage is that the response is standardized by RFC 3659 to YYYYMMDDHHMMSS[.sss]. Disadvantage is that you have to send a separate request for each file, what can be quite inefficient.

Some references:

• C# class to parse WebRequestMethods.Ftp.ListDirectoryDetails FTP response
• Parsing FtpWebRequest ListDirectoryDetails line
• Retrieving creation date of file (FTP)

---

Alternatively, use a 3rd party FTP library that supports the MLSD command, and/or supports parsing of the proprietary listing format.

For example WinSCP .NET assembly supports both.

An example code:

# Load WinSCP .NET assembly
Add-Type -Path "WinSCPnet.dll"

# Setup session options
$sessionOptions = New-Object WinSCP.SessionOptions -Property @{
    Protocol = [WinSCP.Protocol]::Ftp
    HostName = "example.com"
    UserName = "user"
    Password = "mypassword"
}

$session = New-Object WinSCP.Session

# Connect
$session.Open($sessionOptions)

# Get list of files in the directory
$directoryInfo = $session.ListDirectory($remotePath)

# Select the most recent file
$latest =
    $directoryInfo.Files |
    Where-Object { -Not $_.IsDirectory } |
    Sort-Object LastWriteTime -Descending |
    Select-Object -First 1

# Any file at all?
if ($latest -eq $Null)
{
    Write-Host "No file found"
    exit 1
}

# Download the selected file
$sourcePath = [WinSCP.RemotePath]::EscapeFileMask($remotePath + $latest.Name)
$session.GetFiles($sourcePath, $localPath).Check()

For a full code, see Downloading the most recent file (PowerShell).

(I'm the author of WinSCP)