Script to update xml value

I am trying to do update on xml file based on condition using AWK Script. Could anyone assist me on this?

students.xml

<students>
    <student>
        <stuId>1</stuId>
        <name>A</name>
        <mark>75</mark>
        <result></result>
    </student>
    <student>
        <stuId>2</stuId>
        <name>B</name>
        <mark>35</mark>
        <result></result>
    </student>
    <student>
        <stuId>1</stuId>
        <name>C</name>
        <mark>94</mark>
        <result></result>
    </student>
</students>

Code I tried so far

I am able to extract tag values using below code

BEGIN { RS="<[^>]+>" } 
{ print  RT, $0 }

This prints all the tag and values as expected.

I want to update the <result> tag as pass if marks > 40 else fail

Output

<students>
    <student>
        <stuId>1</stuId>
        <name>A</name>
        <mark>75</mark>
        <result>pass</result>
    </student>
    <student>
        <stuId>2</stuId>
        <name>B</name>
        <mark>35</mark>
        <result>fail</result>
    </student>
    <student>
        <stuId>1</stuId>
        <name>C</name>
        <mark>94</mark>
        <result>pass</result>
    </student>
</students>

Could any one assist me on this?

Solution

Don't try to parse XML with awk, instead use a real parser :

the XML file is edited on the fly!

With perl :

#!/usr/bin/env perl
# edit file.xml file in place
use strict; use warnings;

use XML::LibXML;

my $xl = XML::LibXML->new();
my $xml = $xl->load_xml(location => '/tmp/file.xml') ;

for my $node ($xml->findnodes('//student/result')) {
    my $mark = $node->findnodes('../mark/text()')->string_value;
    $node->removeChildNodes();
    if ($mark > 40) {
        $node->appendText('pass');
    }
    else {
        $node->appendText('fail');
    }
}

$xml->toFile('/tmp/file.xml');

Modified file :

<?xml version="1.0"?>
<students>
  <student>
    <stuId>1</stuId>
    <name>A</name>
    <mark>75</mark>
    <result>pass</result>
  </student>
  <student>
    <stuId>2</stuId>
    <name>B</name>
    <mark>35</mark>
    <result>fail</result>
  </student>
  <student>
    <stuId>1</stuId>
    <name>C</name>
    <mark>94</mark>
    <result>pass</result>
  </student>
</students>