In addition to the advice already provided, consider replacing your sequence of print statements by a much simpler and less verbose HERE doc:

open my $fh, '>', $filename or die "Can not open file $filename: $!";
print $fh <<"EOF";
<?xml version="1.0" encoding="UTF-8"?>
<XML TAGS>
<SERIES>$series</SERIES>
<ETC>$etc</ETC>
<ETC>$etc</ETC>
</XMLTAGS>
EOF
close $fh;
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That being said, I second the recommendation to consider using a CPAN module for creating the XML file.