linux xml powershell xpath read-eval-print-loop

How to print a list of xml elements and their properties in the Powershell REPL console?

Referencing:

https://www.red-gate.com/simple-talk/sysadmin/powershell/powershell-data-basics-xml/

and:

https://stackoverflow.com/a/65264118/4531180

how is a list of elements and their properties printed?

PS /home/nicholas/powershell> 
PS /home/nicholas/powershell> $doc = new-object System.Xml.XmlDocument
PS /home/nicholas/powershell> $file = resolve-path('./bookstore.xml') 
PS /home/nicholas/powershell> $doc.load($file)                                           
PS /home/nicholas/powershell> 
PS /home/nicholas/powershell> $doc.bookstore.book[1].author.first-name
ParserError: 
Line |
   1 |  $doc.bookstore.book[1].author.first-name
     |                                     ~~~~~
     | Unexpected token '-name' in expression or statement.

PS /home/nicholas/powershell> 
PS /home/nicholas/powershell> $doc.bookstore.book[1].author           

first-name last-name
---------- ---------
Margaret   Atwood

PS /home/nicholas/powershell> 
PS /home/nicholas/powershell> $doc.bookstore

bk          book
--          ----
urn:samples {book, book, book, book}

PS /home/nicholas/powershell>

Solution

To address the for-display formatting problem:

If you look closely at the sample output from your own answer, you'll see that even though the display is mostly helpful, the value of the author property is author instead of showing the (presumed) first-name and last-name child-element values.

The problem is that PowerShell's default output formatting represents child elements that have:

at least one attribute
and/or at least one child element themselves

by the element's name only.

Especially with deeply nested elements this results in unhelpful output.

Workarounds, possibly in combination:

Access the .OuterXml or .InnerXml property of such elements, which contains the full XML text of the element with / without the element's tags themselves.
- This will likely only be helpful with perhaps at most another level of nesting will be visually helpful, given that the XML text is a single-line representation that is not pretty-printed.
- You can pipe .OuterXml / InnerXml values to a pretty-printing function, which requires some extra work, however, because no such functionality is directly exposed by PowerShell.
Use Select-Object (or, for display purposes only, a Format-* cmdlet such as Format-Table) with calculated properties.
- While this allows you full control over what is displayed, it is more work.

See the examples below.

# Sample XML document
$xmlDoc = [xml] @"
<?xml version="1.0"?>
<bookstore>
   <book id="bk101">
      <author>
        <first-name>Matthew</first-name>
        <last-name>Gambardella</last-name>
      </author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <price>44.95</price>
      <publish_date>2000-10-01</publish_date>
      <description>An in-depth look at creating applications with XML.</description>
   </book>
   <book id="bk102">
      <author>
        <first-name>Kim</first-name>
        <last-name>Rall</last-name>
      </author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-12-16</publish_date>
      <description>A former architect battles corporate zombies, an evil sorceress, and her own childhood to become queen of the world.</description>
   </book>
</bookstore>
"@

To get a helpful representation of all <book> elements including the <author> child elements' <first-name> and <last-name> child elements via Select-Object and a calculated property:

$xmldoc.bookstore.book | Select-Object id, 
   @{ n='author'; e={ $_.author.'first-name' + ' ' + $_.author.'last-name'} }, 
   title, genre, price, publish_date, description

This yields (note how the author property now lists first and last name):

id           : bk101
author       : Matthew Gambardella
title        : XML Developer's Guide
genre        : Computer
price        : 44.95
publish_date : 2000-10-01
description  : An in-depth look at creating applications with XML.

id           : bk102
author       : Kim Rall
title        : Midnight Rain
genre        : Fantasy
price        : 5.95
publish_date : 2000-12-16
description  : A former architect battles corporate zombies, an evil sorceress, and her own childhood to become queen of the world.

To get a helpful representation of all <book> elements via pretty-printed XML, via an auxiliary System.Xml.Linq.XDocument instance:

# Load the assembly that contains XDocument.
# Note: Required in Windows PowerShell only, and only once per session.
Add-Type -AssemblyName System.Xml.Linq

$xmldoc.bookstore.book | ForEach-Object {
  ([System.Xml.Linq.XDocument] $_.OuterXml).ToString()
}

This yields (a pretty-printed XML representation):

<book id="bk101">
  <author>
    <first-name>Matthew</first-name>
    <last-name>Gambardella</last-name>
  </author>
  <title>XML Developer's Guide</title>
  <genre>Computer</genre>
  <price>44.95</price>
  <publish_date>2000-10-01</publish_date>
  <description>An in-depth look at creating applications with XML.</description>
</book>
<book id="bk102">
  <author>
    <first-name>Kim</first-name>
    <last-name>Rall</last-name>
  </author>
  <title>Midnight Rain</title>
  <genre>Fantasy</genre>
  <price>5.95</price>
  <publish_date>2000-12-16</publish_date>
  <description>A former architect battles corporate zombies, an evil sorceress, and her own childhood to become queen of the world.</description>
</book>

Note that you could wrap the formatting code in a simple (filter) function named Format-Xml that you could put in your $PROFILE file (in Windows PowerShell, also place the Add-Type -AssemblyName System.Xml.Linq there, above it):

filter Format-Xml { ([System.Xml.Linq.XDocument] $_.OuterXml).ToString() }

Now the formatting is as simple as:

$xmldoc.bookstore.book | Format-Xml