How to parse HTML table with Powershell Core 7? - html

Question

I have the following code:
$html = New-Object -ComObject "HTMLFile"
$source = Get-Content -Path $FilePath -Raw
try
{
$html.IHTMLDocument2_write($source) 2> $null
}
catch
{
$encoded = [Text.Encoding]::Unicode.GetBytes($source)
$html.write($encoded)
}
$t = $html.getElementsByTagName("table") | Where-Object {
$cells = $_.tBodies[0].rows[0].cells
$cells[0].innerText -eq "Name" -and
$cells[1].innerText -eq "Description" -and
$cells[2].innerText -eq "Default Value" -and
$cells[3].innerText -eq "Release"
}
The code works fine on Windows Powershell 5.1, but on Powershell Core 7 $_.tBodies[0].rows returns null.
So, how does one access the rows of an HTML table in PS 7?

Answer 1

PowerShell (Core), as of 7.3.1, does not come with a built-in HTML parser - and this may never change.
You must rely on a third-party solution, such as the PowerHTML module that wraps the HTML Agility Pack.
The object model works differently than the Internet Explorer-based one available in Windows PowerShell; it is similar to the XML DOM provided by the standard System.Xml.XmlDocument type ([xml])[1]; see the documentation and the sample code below.
# Install the module on demand
If (-not (Get-Module -ErrorAction Ignore -ListAvailable PowerHTML)) {
Write-Verbose "Installing PowerHTML module for the current user..."
Install-Module PowerHTML -ErrorAction Stop
}
Import-Module -ErrorAction Stop PowerHTML
# Create a sample HTML file with a table with 2 columns.
Get-Item $HOME | Select-Object Name, Mode | ConvertTo-Html > sample.html
# Parse the HTML file into an HTML DOM.
$htmlDom = ConvertFrom-Html -Path sample.html
# Find a specific table by its column names, using an XPath
# query to iterate over all tables.
$table = $htmlDom.SelectNodes('//table') | Where-Object {
$headerRow = $_.Element('tr') # or $tbl.Elements('tr')[0]
# Filter by column names
$headerRow.ChildNodes[0].InnerText -eq 'Name' -and
$headerRow.ChildNodes[1].InnerText -eq 'Mode'
}
# Print the table's HTML text.
$table.InnerHtml
# Extract the first data row's first column value.
# Note: #(...) is required around .Elements() for indexing to work.
#($table.Elements('tr'))[1].ChildNodes[0].InnerText
A Windows-only alternative is to use the HTMLFile COM object, as shown in this answer, and as used in your own attempt - I'm unclear on why it didn't work in your specific case.
[1] Notably with respect to supporting XPath queries via the .SelectSingleNode() and .SelectNodes() methods, exposing child nodes via a .ChildNodes collection, and providing .InnerHtml / .OuterHtml / .InnerText properties. Instead of an indexer that supports child element names, methods .Element(<name>) and .Elements(<name>) are provided.

Answer 2

I used the answer above for my solution. I installed PowerHTML.
I wanted to extract the datatable from https://www.dicomlibrary.com/dicom/dicom-tags/ and convert them.
From this:
<tr><td>(0002,0000)</td><td>UL</td><td>File Meta Information Group Length</td><td></td></tr>
To this:
{"00020000", "ULFile Meta Information Group Length"}
$page = Invoke-WebRequest https://www.dicomlibrary.com/dicom/dicom-tags/
$htmldom = ConvertFrom-Html $page
$table = $htmlDom.SelectNodes('//table') | Where-Object {
$headerRow = $_.Element('tr') # or $tbl.Elements('tr')[0]
# Filter by column names
$headerRow.ChildNodes[0].InnerText -eq 'Tag'
}
foreach ($row in $table.SelectNodes('tr'))
{$a = $row.SelectSingleNode('td[1]').innerText.Trim() -replace "`n|`r|\s+", " " -replace "\(",'{"' -replace ",","" -replace "\)",'",'
$c = $row.SelectSingleNode('td[3]').innerText.Trim() -replace "`n|`r|\s+", " "
$b=$row.seletSingleNode('td[2]').innerText.Trim() -replace "`n|`r|\s+", ""; $c = '"'+$b+$c+'"},'
$row = New-Object -TypeName psobject
$row | Add-Member -MemberType NoteProperty -Name Tag -Value $a
$row | Add-Member -MemberType NoteProperty -Name Value -Value $c
[array]$data += $row
}
$data | Out-File c:\scripts\dd.txt