Simple PHP Script to parse Wordpress posts xml export to get the relative url and prepare for Joomla! com_redirects, note using J2XML with WP Import plugin to import content quickly.

wpExportParseUrlRedirect.php

<?php

// Make sure the WP File is called wpxmlfile.xml 

$xmlfile  = file_get_contents('wpxmlfile.xml');
$wpfile   = simplexml_load_string($xmlfile)->channel;

// Set the parent menu item alias for the posts to be accessed under
// Assumed at present it is 'News with the alias news'
$newParentAlias = '/news/';

// Auto get the link
$url = $wpfile->link;

echo '<strong>Total ITEMS: </strong> ' . count($wpfile->item) . '<br />';

// Just copy and paste the below into com_redirects bulk importer. Not using , 
// as the seperator you may want to change to | for standard J! com_redirects
// But this is configurable in com_redirect global config. 

foreach ($wpfile->item AS $item) {
	$relativeLink	= str_replace($url, '', $item->link);
	$exp_link = explode('/', $relativeLink)[3];
	
	echo $relativeLink . ',' . $newParentAlias . $exp_link . "<br/>";
}

// Debug, comment out below lines
// echo '<pre>';
// print_r($wpfile->channel);