I want to enrich an xml document with new elements and preserve earlier markup.

The script below achieves what I want, but I doubt that my method is safe and proper, as I circumvent LibXML's DOM in the decisive parts of the script.

Could you guide me to a better method? Is an xpath-expression with findnodes the way out?

In the example I look for, and markup, animals and their attributes.
"quick brown fox" is in a tight tag situation and I cannot but indicate it with milestones.
"lazy dog" can be tagged regularly.

Any comment on any part of the script will be very much appreciated. Thank you.


#!/usr/bin/perl

# Catch the canid in 
# "The quick brown fox jumps over the lazy dog."

use strict;
use 5.010;    
use XML::LibXML;
use List::MoreUtils qw(uniq);

my $xml = "<foo>The quick br<bar>o</bar>wn <baz>f<bar>o</bar>x</baz>";
$xml .= " jumps over the lazy d<bar>o</bar>g.</foo>";

my $new_element = "canid";
my @queried = ("quick brown fox","lazy dog");
$xml = &doubtful_method($xml,$_) foreach @queried;

my $dom = XML::LibXML->load_xml( string => $xml);
say $dom->to_literal;

my @canids = 
    uniq map { &catch_milestone($_) } ($dom->findnodes('//canid'));
say "Canids addressed: ", join ", ", @canids;

sub doubtful_method {
    my $xml = $_[0];
    my $queried = $_[1];
    my $rex = join "(<.+?>)?", split //, $queried;
    $xml =~ s/($rex)/&evaluate_match($1)/gem;
    return $xml;
}

sub evaluate_match {
    my $match = $_[0];
    my $out;
    eval { 
        XML::LibXML->load_xml(string => "<test>".$match."</test>") 
    };
    if (ref($@)){
        my $milestone = qq|<$new_element time="| . time . qq |"/>|;
        $out = $milestone.$match.$milestone;
    } else {
        $out = "<$new_element>$match</$new_element>";
    }
    return $out;
}

sub catch_milestone {
    my $node = $_[0];
    my ($out);
    if ($node->hasAttribute("time")) {
        my $milestone = qq|<$new_element(.+?)?time="|;
        $milestone.= $node->getAttribute("time") . qq|"(.+?)?>|;
        my $rex = $milestone . "(?<new>.+?)" . $milestone;
        $out = $+{new} if $dom->documentElement->toString =~ /($rex)/;
        $out =~ s/<.+?>//gm;
    } else {    
        $out = $node->to_literal;
    }
    return $out;
}

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In reply to LiBXML: New markup while preserving earlier tags? by Samantabhadra

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