Retrieve text in HTML with powershell

Question

In this html code :

<div id="ajaxWarningRegion" class="infoFont"></div>
  <span id="ajaxStatusRegion"></span>
  <form enctype="multipart/form-data" method="post" name="confIPBackupForm" action="/cgi-bin/utilserv/confIPBackup/w_confIPBackup" id="confIPBackupForm" >
    <pre>
      Creating a new ZIP of IP Phone files from HTTP/PhoneBackup 
      and HTTPS/PhoneBackup
    </pre>
    <pre> /tmp/IP_PHONE_BACKUP-2012-Jul-25_15:47:47.zip</pre>
    <pre>Reports Success</pre>
    <pre></pre>
    <a href =  /tmp/IP_PHONE_BACKUP-2012-Jul-25_15:47:47.zip>
      Download the new ZIP of IP Phone files
    </a>
  </div>

I want to retrieve the text IP_PHONE_BACKUP-2012-Jul-25_15:47:47.zip or just the date and hour between IP_PHONE_BACKUP- and .zip

How can I do that ?

Answer 1

What makes this question so interesting is that HTML looks and smells just like XML, the latter being much more programmably palatable due to its well-behaved and orderly structure. In an ideal world HTML would be a subset of XML, but HTML in the real-world is emphatically not XML. If you feed the example in the question into any XML parser it will balk on a variety of infractions. That being said, the desired result can be achieved with a single line of PowerShell. This one returns the whole text of the href:

Select-NodeContent $doc.DocumentNode "//a/@href"

And this one extracts the desired substring:

Select-NodeContent $doc.DocumentNode "//a/@href" "IP_PHONE_BACKUP-(.*)\.zip"

The catch, however, is in the overhead/setup to be able to run that one line of code. You need to:

• Install HtmlAgilityPack to make HTML parsing look just like XML parsing.
• Install PowerShell Community Extensions if you want to parse a live web page.
• Understand XPath to be able to construct a navigable path to your target node.
• Understand regular expressions to be able to extract a substring from your target node.

With those requirements satisfied you can add the HTMLAgilityPath type to your environment and define the Select-NodeContent function, both shown below. The very end of the code shows how you assign a value to the $doc variable used in the above one-liners. I show how to load HTML from a file or from the web, depending on your needs.

Set-StrictMode -Version Latest
$HtmlAgilityPackPath = [System.IO.Path]::Combine((Get-Item $PROFILE).DirectoryName, "bin\HtmlAgilityPack.dll")
Add-Type -Path $HtmlAgilityPackPath

function Select-NodeContent(
    [HtmlAgilityPack.HtmlNode]$node,
    [string] $xpath,
    [string] $regex,
    [Object] $default = "")
{
    if ($xpath -match "(.*)/@(\w+)$") {
        # If standard XPath to retrieve an attribute is given,
        # map to supported operations to retrieve the attribute's text.
        ($xpath, $attribute) = $matches[1], $matches[2]
        $resultNode = $node.SelectSingleNode($xpath)
        $text = ?: { $resultNode } { $resultNode.Attributes[$attribute].Value } { $default }
    }
    else { # retrieve an element's text
        $resultNode = $node.SelectSingleNode($xpath)
        $text = ?: { $resultNode } { $resultNode.InnerText } { $default }
    }
    # If a regex is given, use it to extract a substring from the text
    if ($regex) {
        if ($text -match $regex) { $text = $matches[1] }
        else { $text = $default }
    }
    return $text
}

$doc = New-Object HtmlAgilityPack.HtmlDocument
$result = $doc.Load("tmp\temp.html") # Use this to load a file
#$result = $doc.LoadHtml((Get-HttpResource $url)) # Use this  PSCX cmdlet to load a live web page