#!/usr/bin/perl

use strict;
use warnings;

my $file = 'test.xml';

open my $fh, '<', $file or die $!;
while ( my $line = <$fh> ) {
    # benutze den Flip-Flop-Operator http://reneeb-perlblog.blogspot.de/2010/01/der-flip-flop-operator.html
    if ( $line =~ /<fehler>/ .. $line =~ /<\/fehler>/ ) {
        sende_mail() if $line =~ /[1-9]/;
    }
}
close $fh;