PowerShell get first line of node and associated line number

Question

Given XML such as

<?xml version="1.0"?>
<Products>
    <Product_Group id="Robot">
        <Product id="RSAPRO2017">
            <DefaultShortcut>Autodesk Robot Structural Analysis Professional 2017.lnk</DefaultShortcut>
            <ProgramFolder>C:\Program Files\Autodesk\Autodesk Robot Structural Analysis Professional 2017</ProgramFolder>
            <UserAppDataRoaming>C:\Users\$(userName)\AppData\Roaming\Autodesk\Autodesk Robot Structural Analysis Professional 2017</UserAppDataRoaming>
        </Product>
    </Product_Group>
</Products>

And a PowerShell variable $node using SelectSingleNode to select the Product, is there a way to 1: Get just the first line of the node, so <Product id="RSAPRO2017">, and 2: Get the line number in the XML, so in this example line # would be 4.

I can show an approximation for #1 with Write-Host "<$($node.name)>" but that doesn't provide the full line.

The goal here is to validate some complex XML and provide an error log with details that allow a person to revise their XML quickly and easily. So, for example, since the right node name is Product I might have an error log of

Invalid node (Productt) at line 4
    <Productt id="RSAPRO2017">

I can get the OuterXML of the entire node, but some nodes have 40-50 lines so that's no help. I could extract the first line with a RegEx to get everything between the first < > pair, but I wonder if there is a built in PowerShell/XPath approach, rather than rolling my own? And, getting the line number seems... iffy in general.

Answer 1

As @BACON commented, an xml reader in PowerShell will throw an exception if the xml is malformed. The [xml] type implementation in PowerShell shows this:

[xml]$malformed = @'
<?xml version="1.0"?>
<Products>
    <Product_Group id="Robot">
        <Productt id="RSAPRO2017">
            <DefaultShortcut>Autodesk Robot Structural Analysis Professional 2017.lnk</DefaultShortcut>
            <ProgramFolder>C:\Program Files\Autodesk\Autodesk Robot Structural Analysis Professional 2017</ProgramFolder>
            <UserAppDataRoaming>C:\Users\$(userName)\AppData\Roaming\Autodesk\Autodesk Robot Structural Analysis Professional 2017</UserAppDataRoaming>
        </Product>
    </Product_Group>
</Products>
'@

Yields output which includes:

Error: "The 'Productt' start tag on line 4 position 10 does not match the end tag of 'Product'.

If you want to be a bit smarter about what you do with the error information, wrap the whole thing inside try {} catch {} and try to extract data from the automatic $Error array, of which the most recent error is held at position zero ($Error[0]).

try {} attempts to do something and catch {} only runs if the attempt failed. You can also add finally {} to do something after catch regardless of error/success.

try {
[xml]@'
<?xml version="1.0"?>
<Products>
    <Product_Group id="Robot">
        <Productt id="RSAPRO2017">
            <DefaultShortcut>Autodesk Robot Structural Analysis Professional 2017.lnk</DefaultShortcut>
            <ProgramFolder>C:\Program Files\Autodesk\Autodesk Robot Structural Analysis Professional 2017</ProgramFolder>
            <UserAppDataRoaming>C:\Users\$(userName)\AppData\Roaming\Autodesk\Autodesk Robot Structural Analysis Professional 2017</UserAppDataRoaming>
        </Product>
    </Product_Group>
</Products>

'@}
catch {
$Error[0].Exception.Message
}

Answer 2

Though this really seems like a job for validating against a schema file (in which case see How do I use PowerShell to Validate XML files against an XSD?), if you want to perform hard-coded validation you can use the XDocument class to get line information.

However you obtain an XDocument instance ([System.Xml.Linq.XDocument]::Load() or [System.Xml.Linq.XDocument]::Parse()), you'll need to pass a [System.Xml.Linq.LoadOptions] value specifying that you want line information to be tracked. Line information is made available via the IXmlLineInfo interface which is explicitly implemented by the XObject class and its descendants, though in PowerShell you can access its members automagically.

Given SO59240313.xml...

<?xml version="1.0"?>
<Products>
    <Product_Group id="Robot">
        <Product id="RSAPRO2017">
            <DefaultShortcut>Autodesk Robot Structural Analysis Professional 2017.lnk</DefaultShortcut>
            <ProgramFolder>C:\Program Files\Autodesk\Autodesk Robot Structural Analysis Professional 2017</ProgramFolder>
            <UserAppDataRoaming>C:\Users\$(userName)\AppData\Roaming\Autodesk\Autodesk Robot Structural Analysis Professional 2017</UserAppDataRoaming>
        </Product>
        <Productt id="SomeId">
            <DefaultShortcut>Some shortcut</DefaultShortcut>
            <ProgramFolder>Some program path</ProgramFolder>
            <UserAppDataRoaming>Some roaming path</UserAppDataRoaming>
        </Productt>
    </Product_Group>
</Products>

...this code...

function ReportUnexpectedElement([System.Xml.Linq.XElement] $element)
{
    Write-Warning "Unexpected element ""$($element.Name)"" found at position $($element.LinePosition) of line $($element.LineNumber)."
}

$document = [System.Xml.Linq.XDocument]::Load(
    "$PWD\SO59240313.xml",
    [System.Xml.Linq.LoadOptions]::SetLineInfo
)

if ($document.Root.Name -ne 'Products')
{
    ReportUnexpectedElement $document.Root
}
else
{
    $productGroupElement = $document.Root.Element('Product_Group')
    if ($null -eq $productGroupElement)
    {
        Write-Warning 'Product_Group element not found.'
    }
    else
    {
        foreach ($productGroupChildElement in $productGroupElement.Elements())
        {
            if ($productGroupChildElement.Name -ne 'Product')
            {
                ReportUnexpectedElement $productGroupChildElement
            }
        }
    }
}

...will print this output...

WARNING: Unexpected element "Productt" found at position 4 of line 9.

I'm not seeing a readily-accessible way to retrieve an element's complete opening tag, but you could reconstruct it yourself by modifying the ReportUnexpectedElement function like this...

function ReportUnexpectedElement([System.Xml.Linq.XElement] $element)
{
    $elementBuilder = New-Object -TypeName 'System.Text.StringBuilder'

    # Most StringBuilder methods return a reference to that same instance,
    # so remember to suppress them from the function output
    $elementBuilder.Append('<').Append($element.Name) `
        | Out-Null
    foreach ($attribute in $element.Attributes())
    {
        $elementBuilder.AppendFormat(' {0}="{1}"', $attribute.Name, $attribute.Value) `
            | Out-Null
    }
    $elementBuilder.Append('>') `
        | Out-Null

    Write-Warning "Unexpected element ""$($elementBuilder.ToString())"" found at position $($element.LinePosition) of line $($element.LineNumber)."
}

...which, given the same XML file, will print this output...

WARNING: Unexpected element "<Productt id="SomeId">" found at position 4 of line 9.