unless ($basename =~ /^(.{4}|.{10})_(.{10})_(.{8})_(.{6})_(.{10})_(.{8})\.(.{3})(\.gz)?$/) {
    # ...

##</code><code>##

# Validate Filename Structure
if ($basename =~ /^(.{4}|.{10})_(.{10})_(.{8})_(.{6})_(.{10})_(.{8})\.(.{3})(\.gz)?$/) {
    #
    # File Name Format Fits
    #
    ($issuercode, $outputname, $date, $time, $userid, $sequenceno, $filetype) =
        ($1, $2, $3, $4, $5, $6, $7);

}
else {
    if ((system @COPY, $filename, sprintf "%s%s%s%s", $UNHANDLED, $delimiter, $basename, $dupe_extn) == 0) {
        abort __LINE__,"bad filename '$filename', moved to unhandled directory";
    }
    else {
        abort __LINE__,"failed to move unhandled file '$filename'!";
    }
}