#!/bin/perl -w
use strict;

use XML::XPath;
              
my @results;

# create the xpath object from the DATA filehandle
my $xp = XML::XPath->new( ioref => \*DATA);
              
# find all paragraphs
my $elts = $xp->find('/doc/elt'); 
              
foreach my $elt ($elts->get_nodelist) 
  { # there is probably a more elegant way to get the child children
    # but I don't know XML::XPath enough
    my $children= $elt->getChildNodes;                         # get all children
    my @children= grep { $_->getName eq 'child' } @$children;  # grep only the relevant ones
    if( @children)
      { push @results, $children[0]->string_value; }           # that's how you get the text
    else
      { push @results, "missing child for elt " . $elt->getAttribute( 'id'); }
   } 
print join "\n", @results;
print "\n";

__DATA__
<doc>
  <dummy>I am a </dummy>
  <elt id="elt1"><child_1/><child>child 1</child></elt>
  <elt id="elt2"><child_1/></elt>
  <elt id="elt3"><child_1/><child>child 2</child></elt>
  <elt id="elt4"><child_1/></elt>
</doc>