XML::LibXML replace value - perl

Question

I have the below xml file and in this I want to write a perl script so that I can grep on first book name and then author name and if both of them matches change the field "value" from false to true. For ex if book name is abc and author name is john, change the value from false to true.
use warnings;
use strict;
use XML::LibXML;
my $parser = XML::LibXML->new();
my $xmldoc = $parser->parse_file('b.xml');
for my $book ($xmldoc->findnodes('/library/book')) {
my $name = $book->findvalue('/#name');
if($name eq "abc")
{
print "yes" ;
}
}
<library>
<book name="abc" id="3">
<key name="history">
<default label="base" value="1"/>
</key>
<author name="john">
<default label="base" value="false"/>
</author>
</book>
<book name="xyz" id="4">
<key name="science">
<default label="base" value="1"/>
</key>
<author name="nik">
<default label="base" value="false"/>
</author>
</book>
I am new to perl, can someone help me here? I have written some code to reach to first point to check the author name but that itself is not working.

Answer 1

for my $default_author_node ($xmldoc->findnodes(
'/library/book[#name="abc"]/author[#name="john"]/default'
)) {
$default_author_node->setAttribute('value', 'true');
}
But you probably want the names to be variable.
Solution 1: Dynamically build the above XPath.
sub text_to_xpath {
my ($s) = #_;
return qq{"$s"} if $s !~ tr/"//;
return qq{'$s'} if $s !~ tr/'//;
$s = s/"/", '"', "/g;
return qq{concat("$s")};
}
my $target_book_xp = text_to_xpath($target_book);
my $target_author_xp = text_to_xpath($target_author);
for my $default_author_node ($xmldoc->findnodes(
"/library/book[\#name=$target_book_xp]/author[\#name=$target_author_xp]/default"
)) {
$default_author_node->setAttribute('value', 'true');
}
Solution 2: Do the checking yourself.
This is what you were attempting, but XPath /#name gets the child attributes (#) named name at the root of the document (/), but the only node there is the root element (library). Just like in directory paths, don't use a leading / if you want to search relative to the context.
for my $book_node ($xmldoc->findnodes('/library/book')) {
my $name = $book_node->getAttribute('name');
next if !defined($name) || $name ne $target_book;
for my $author_node ($book_node->findnodes('author')) {
my $name = $book_node->getAttribute('name');
next if !defined($name) || $name ne $target_author;
for my $default_author_node ($author_node->findnodes('default')) {
$default_author_node->setAttribute('value', 'true');
}
}
}