# parsing File 1
my @nodes_from_file1 = $parser->findnodes('//Feature');
# or whatever it is you need in each node

# later
my $new = XML::LibXML::Document->new('1.0', 'utf-8');
my $features = $new->createElement( 'Features' );
my $file1 = $new->createElement( 'File1' );
for my $node (@nodes_from_file1) {
    $file1->addChild( $node );
}
$features->addChild( $file1 );
# and so on
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<Features>
  <File1>
    <Feature>
        <Number>86839</Number>
        <Prefix>419</Prefix>
        <Alt>73924</Alt>
    </Feature>
    <Feature>
        <Number>82783</Number>
        <Prefix>826</Prefix>
        <Alt>27800</Alt>
    </Feature>
    <Feature>
        <Number>82783</Number>
        <Prefix>827</Prefix>
        <Alt>26433</Alt>
    </Feature>
  </File1>
</Features>
[download]

Thanks for your help. I was trying your soltuion but I cant figure out the follwoing:
1. how I can view my output file? I don't see any generated output files
2. I assume "parser" in this case will be parsing the source file (where im getting my input from) right ?

I understand whats going on with your code but im just lost with where I see my results. I have tried multiple times but couldn't see any generated output file.
tried different examples using the same approach but still cant figure out how to get my output file.

how I can view my output file? I don't see any generated output files

You can print directly to a file using the toFile() method. Add the following lines to the example given above:

$new->addChild($features);
my $filename = 'new.xml';
my $ok = $new->toFile($filename,2);
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I assume "parser" in this case will be parsing the source file (where im getting my input from) right?

Yes, you would set up the parser like this, probably in a loop to go through each file:

my $file = 'file-1.xml';
my $parser = XML::LibXML->load_xml(location => $file);
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Here is my code:

use XML::LibXML;

my $parser = XML::LibXML->new();
my $doc = $parser->parse_file("FILE1.xml");

my @nodes_from_file1 = $doc->findnodes('//Feature');

my $new = XML::LibXML::Document->new('1.0', 'utf-8');

my $features = $new->createElement( 'Features' );

#print to debug 
print $features->toString;

my $file1 = $new->createElement( 'File1' );

for my $node (@nodes_from_file1) {
    $file1->addChild( $node );
    
    #print to debug
    print $file1->toString;
    
}
$features->addChild( $file1 );

print $new->toString;
$new->toFile("output_new.xml")
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I can't see the line $new->addChild($features);

You need to include the format argument 2 in $new->toFile("output_new.xml",2) and print $new->toString(2);

If you're mostly just copying the contents of several files, perhaps consider not using a module at all. Something along the lines of this code (following some Notes) might do what you want.

Notes:

• You didn't specify exactly which parts of the source files were to be copied. I'll leave you to make changes depending on your requirements.
• IDs should be unique. I've added code to do this. Again, modify how you want.
• I've added consistent indentation. You may want something different: change to suit.
• Assumed a typo: s{<doc/>}{</doc>}
• I've used a cut-down version of your data for demo purposes.
• I'll leave you to replace Inline::Files and \*STDOUT with more appropriate I/O.

#!/usr/bin/env perl -l

use strict;
use warnings;

use Inline::Files;

my %doc_fh_for = (File0 => \*FILE0, File1 => \*FILE1, File2 => \*FILE2
+);
my $out_fh = \*STDOUT;
my $key_file = 'File0';
my @feature_files = qw{File1 File2};

print $out_fh '<Key="1234">';
write_xml_content($key_file, $doc_fh_for{$key_file}, $out_fh, ' ' x 4)
+;
print $out_fh '    <Status="in use"/>
    <Features>';
for (@feature_files) {
    write_xml_content($_, $doc_fh_for{$_}, $out_fh, ' ' x 8);
}
print $out_fh '    </Features>
    <Other_Status/>
</Key>';

sub write_xml_content {
    my ($file_id, $in_fh, $out_fh, $indent) = @_;
    
    while (<$in_fh>) {
        chomp;

        if (/^<\/?doc>$/) {
            s/doc/$file_id/;
        }
        else {
            if (/^<ABC id="(\d+)">$/) {
                my $id = $1;
                s/$id/$file_id-$id/;
            }
            $_ = ' ' x 4 . $_;
        } 

        print $out_fh $indent, $_;
    }
}
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Inline::Files data:

__FILE0__
<doc>
<ABC id="1">
    <Feature>
        <Number>86839</Number>
    </Feature>
</ABC>
<ABC id="2">
    <Feature>
        <Number>82783</Number>
    </Feature>
</ABC>
</doc>
__FILE1__
<doc>
<ABC id="1">
    <Feature>
        <Number>86839</Number>
    </Feature>
</ABC>
<ABC id="2">
    <Feature>
        <Number>82783</Number>
    </Feature>
</ABC>
</doc>
__FILE2__
<doc>
<ABC id="1">
    <Feature>
        <Number>86839</Number>
    </Feature>
</ABC>
<ABC id="2">
    <Feature>
        <Number>82783</Number>
    </Feature>
</ABC>
</doc>
[download]

Output:

well, you actually got exactly what im looking for. By taking a look at your code and the output example you provided, I can tell that you exactly understand what I am aiming at. Easy to track steps
I'm working on it right now and I hope I can generate my desired output as you explained

After looking into this solution I realized the use of Inline::Files is only for small virtual files. But in my case eahc of my file is hundreds of lines.
anyway this can be modified to read the 3 files at the same time and grab information by ID, instead of inline files ?
plus im having issues install the Inline::File module...Thanks for your help

The use of Inline::Files and \*STDOUT was simply for demo purposes; hence the "I'll leave you to replace Inline::Files and \*STDOUT with more appropriate I/O.".

I'm not sure whether you've got a handle on this. If you have, you probably won't need the following; if not, here's some hints and tips that may prove useful for your real code. Ask if you need more information, further explanation, etc.

I'd recommend the autodie pragma. This will save a lot of effort checking whether files could be opened, created, read, written and so on. Put it near the top of your code; I usually write this:

...
use strict;
use warnings;
use autodie;
...
[download]

Remove the 'use Inline::Files; line.

Use open to create your filehandles.

The output filehandle ($out_fh) is very straightforward:

open my $out_fh, '>', '/path/to/output_file';
[download]

The input filehandles are a little more complicated but still fairly easy. I wouldn't recommend creating all the filehandles in advance; instead, open and close one at a time. The \*FILE0, \*FILE1, etc. in my original code are filehandles for the Inline::Files: you'll see I didn't need to explicitly create those. Perhaps change:

my %doc_fh_for = (File0 => \*FILE0, File1 => \*FILE1, File2 => \*FILE2
+);
[download]

to something like this

my %source_file_for = (File0 => 'filename0', File1 => 'filename1', Fil
+e2 => 'filename2');
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and then further down

for (@feature_files) {
    open my $in_fh, '<', $source_file_for{$_};
    write_xml_content($_, $in_fh, $out_fh, ' ' x 8);
    close $in_fh;
}
[download]

I don't know whether you have a predetermined list of source files or if you have to find them in one or more directories; if the latter, you may find readdir useful for this. Also note that may need to prefix the filenames with directory paths: while simple concatenation may suffice, I'd normally use File::Spec as it's portable (it's also a core module so there's no need to install it).

-- Ken

I just don't know how to copy the element itself.

Why not? XML::LibXML::Element -> XML::LibXML::Node#cloneNode, appendChild ...

Hey...Thanks all for the help I will work on this and see what I get. I guess what you all have provided is very helpful.