Maybe a bit late, but one has to sleep sometimes. Here is the Proper Way™, i.e. using a pull-parser to process the huge XML: 
#!/usr/bin/perl
use warnings;
use strict;

use XML::LibXML::Reader;

open my $TXT, '<', '1.txt' or die $!;
my %ids;
while (<$TXT>) {
    undef $ids{ (split /,/)[5] };
}
close $TXT;

my $xml = XML::LibXML::Reader->new( location => '1.xml' )
    or die "Cannot open xml\n";

while ($xml->nextElement('ALERT_ID')) {
    $xml->read;             # Go to the text value.
    my $id = $xml->value;

    if (exists $ids{$id}) {
        delete $ids{$id};

    } else {
        warn "Not found in csv: $id\n";
    }
}
print "$_\n" for keys %ids;

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In reply to Re: Seaching for text in string and comparing to xml, if not found print text by choroba
in thread Seaching for text in string and comparing to xml, if not found print text by helpneeded

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