I was planning to learn Powershell for some time now and this seemed like a good opportunity to learn a few basic things: we had a txt file with urls of multiple images (one per line) and needed to download them while preserving directory structure. Below is the powershell script with comments. Things that it illustrates:

• Using System.Net.WebClient
• Join-Path helper
• 2.0 error handling using try/catch

$webclient = New-Object System.Net.WebClient                        

$dest = "D:\temp"            

$errors = @()            

$images = (get-content $dest"\images.txt")                        

for ($i=0; $i -le $images.Length – 1; $i++) {
    $url = $images[$i]                        

    # DownloadFile doesn't like spaces
    $url = $url.toString().trim();            

    # also requires "http://" for URL
    if ($url.indexOf("http://") -eq -1) {
        $url = "http://" + $url
    }            

    Write-Host ($i + 1) " / " $images.Length " : " $url            

    if ($url -ne "") {
        # Example URL: http://www.example.com/aaaa/bbb/image.jpg            

        # requirement was to preserve the folder structure
        # removing http://            
        $str = $url.replace("http://", "")         # www.example.com/aaaa/bbb/image.jpg            

        # removing domain name
        $str = $str.substring($str.indexOf("/"))   # /aaaa/bbb/image.jpg
        $str = $str.replace("/", "\")              # \aaa\bbb\image.jpg            

        # determining folder structure by removing file name            
        $dir = $str.substring(0, $str.lastIndexOf("\"))            # \aaaa\bbb            

        # if folder doesn't exist locally, create it
        $imageDir = Join-Path $dest $dir
        if (!(test-path $imageDir -pathtype container)) {
            # md create full folder strucutre if provided. 
            # Example: D:\A\B\C\D will create all subfolders
            md $imageDir
        }            

        $localImagePath = Join-Path $dest $str
        Write-Host $localImagePath            

        #http://stackoverflow.com/questions/2182666/powershell-2-0-try-catch-how-to-access-the-exception
        try {
            $webclient.DownloadFile($url, $localImagePath)
        }
        catch [Exception] {
            $errors += $url
            Write-Host "ERROR: " + $_.Exception.ToString() -foregroundcolor "red"
        }
    }
}
Write-Host "done. errors: "
$errors