#!/usr/bin/perl -w
use strict;

use XML::Twig;

my $USAGE= "$0 <file> <path_to_update> <value>";
die $USAGE unless( @ARGV == 3);

my( $file, $path, $value)= @ARGV;

# $_ is set to the current element in the handler
# you could also delete the element after printing it
# for even less memory usage
my $twig= XML::Twig->new( twig_roots => { $path => sub { $_->set_text( $value); $_->print; } },
                          twig_print_outside_roots => 1,
                        );
$twig->parsefile( $file);