Do not use regexes for this job. You will get bitten by all the edge-cases.

One possible solution uses the XML::XPath-module and uses XPath expressions to traverse the xml-file.

/descendant-or-self::comment() therefore selects all comment nodes in or under the root node, i.e. all comment nodes in the whole file.
use strict;
use warnings;

use XML::XPath;

my $xml = q|<?xml version="1.0" ?>
<xml><!-- A single line comment -->

<class_list>
    <student>
        <name>Robert</name>
        <!-- A comment deeply inside the file -->
        <grade>A+</grade>
    </student>
<!-- Here starts a multi line comment
    <student>
        <name>Lenard</name>
        <grade>A-</grade>
    </student>
-->
</class_list>
</xml>
|;

my $xp = XML::XPath->new(xml => $xml);

my $nodeset = $xp->find('/descendant-or-self::comment()');

foreach my $node ($nodeset->get_nodelist) {
    print "FOUND\n",
        $node->getValue,
        "\n";
}

[download]
Output:
FOUND
 A single line comment 
FOUND
 A comment deeply inside the file 
FOUND
 Here starts a multi line comment
    <student>
        <name>Lenard</name>
        <grade>A-</grade>
    </student>

[download]

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In reply to Re: Perl pattern matching by CountZero
in thread Perl pattern matching by Rahul205

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