R – How to add an attribute to a child element using Perl’s XML::Twig

perlxmlxml-twig

I have an XML string like this:

<DATA>
   <CHILD_DATA ATVAL="value1"/>
   <CHILD_DATA />
</DATA>

The final output I want is:

<DATA>
   <CHILD_DATA ATVAL="value1"/>
   <CHILD_DATA ATVAL="value2"/>
</DATA>

My twig $t is at <DATA>. Now I want to add an attribute to the second <CHILD_DATA />. The attribute is ATVAL="value2". I tried the following:

$t->last_child('CHILD_DATA')->set_att{"ATVAL","value2"};

This didn't work. What's wrong with this code? Is there another way to do this?

Best Answer

As Jon hinted to you, you have a syntax error in the code you posted. You should have seen a compile error like:

syntax error at test line 18, near "->set_att{" Execution of program.pl aborted due to compilation errors.

However, you might have typed the code into your answer so that code doesn't match what you are actually doing. Always put the actual code into your question rather than re-typing it, and always post a full program when you can. When you post your program, I don't have to start from scratch to debug what I think you might be doing. :)

Here's a program that does what you want:

use XML::Twig;

my $xml = <<'XML';
<DATA>
   <CHILD_DATA ATVAL="value1"/>
   <CHILD_DATA />
</DATA>
XML

my $twig= XML::Twig->new( keep_spaces => 1 );

$twig->parse( $xml );

$twig
    ->root
    ->last_child('CHILD_DATA')
    ->set_att("ATVAL" => "value2");

$twig->flush;

Related Solutions

XML attribute vs XML element

I use this rule of thumb:

An Attribute is something that is self-contained, i.e., a color, an ID, a name.
An Element is something that does or could have attributes of its own or contain other elements.

So yours is close. I would have done something like:

EDIT: Updated the original example based on feedback below.

  <ITEM serialNumber="something">
      <BARCODE encoding="Code39">something</BARCODE>
      <LOCATION>XYX</LOCATION>
      <TYPE modelNumber="something">
         <VENDOR>YYZ</VENDOR>
      </TYPE>
   </ITEM>

R – How to add child elements to XML using Perl’s XML::Twig

Here is a solution incorporating what I think are reasonable fixes to your question. The code below is based on the filtering example given in the documentation.

#!/usr/bin/perl

use strict;
use warnings;

use XML::Twig;

my $t = XML::Twig->new(
    twig_roots => { SERVER => \&update },
    twig_print_outside_roots => 1,
);

$t->parse(\*DATA);

sub update {
    my ($t, $server) = @_;
    if ( 'serv2' eq $server->att('HOSTNAME') ) {
        $server->insert(
            CIFS_SERVICE => { NETBIOSNAME => 'serv2' },
        );
    }
    $server->print;
}


__DATA__
<SOURCE_SERVER>
  <SERVER HOSTNAME="serv1">
      <CIFS_SERVICE NETBIOSNAME="serv1" />
  </SERVER>
  <SERVER HOSTNAME="serv2">
  </SERVER>
</SOURCE_SERVER>

Output:

C:\Temp> x
<SOURCE_SERVER>
  <SERVER HOSTNAME="serv1"><CIFS_SERVICE NETBIOSNAME="serv1"/></SERVER>
  <SERVER HOSTNAME="serv2"><CIFS_SERVICE NETBIOSNAME="serv2"/></SERVER>
</SOURCE_SERVER>

Best Answer

Related Solutions

XML attribute vs XML element

R – How to add child elements to XML using Perl’s XML::Twig

Related Topic