This doesn't look right:

my $sqlstmt = "select to_date('$tdate','mm/dd/yyyy') from dual";
my $sth = $dbh->prepare($sqlstmt);
$sth->execute() or die $dbh->errstr;
my $tmp;
$sth->bind_columns(undef, \$tmp);
while($sth->fetch()) {$tdate = $tmp;}
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bind_columns binds columns to a list of variables. You're selecting one "column", and binding it to two "variables" (the first one is undef).

undef is probably getting translated to placeholder number zero(oops, I'm confusing myself w/bind_col vs bind_columns...but the following still holds), you want:

$sth->bind_col(1, \$tmp);
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Read the docs, bind_col and bind_columns are slightly different, and bind_col values start at 1, not 0.