$ cat file_<ID>.xml
...
 ...
   ...
      <double>1.2342</double>
      <double>2.3456</double>
      ...
   ...
 ...
...

file_0001 1.2342 2.3456 ...
file_0002 1.2342 2.3456 ...

./from_xml_to_csv.sh  100.45s user 94.84s system 239% cpu 1:21.48 total

find . ! -name . -prune -name pattern -type f -exec cat {} + | ...

#!/usr/bin/env perl

use strict;
use warnings;
use XML::Twig;

my $twig = XML::Twig -> new;
$twig -> parse ( *DATA );

foreach my $double ( $twig -> get_xpath('//double') ) {
   print $double -> trimmed_text,"n";
}

__DATA__
<root>
 <subnode>
   <another_node>
      <double>1.2342</double>
      <double>2.3456</double>
      <some_other_tag>fish</some_other_tag>
   </another_node>
 </subnode>
</root>

1.2342
2.3456

#!/usr/bin/env perl

use strict;
use warnings;
use XML::Twig;
use Text::CSV;

my $twig = XML::Twig->new;
my $csv  = Text::CSV->new;

#open our results file
open( my $output, ">", "results.csv" ) or die $!;
#iterate each XML File.
foreach my $filename ( glob("/path/to/xml/*.xml") ) {
    #parse it
    $twig->parsefile($filename);
    #extract all the text of all the 'double' elements.
    my @doubles = map { $_->trimmed_text } $twig->get_xpath('//double');
    #print it as comma separated.
    $csv->print( $output, [ $filename, @doubles ] );

}
close($output);

get_xpath("/root/subnode/another_node/double")

for f in `ls *.xml` ;
do
     echo $f,`grep double $f | awk  -F  '[<>]' '{print $3}' | tr 'n' ','`;
done