You probably don't need a constant constant for this; just use a variable. This will simplify your connection string, since you can then use Perl's built-in variable interpolation instead of the clunkier concatenation with a constant value:

our $DBNAME = 'database_test';

my $dbh = DBI->connect("DBI:mysql:database=$DBNAME", 'username', 'pass
+word') or die;
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Note the single-quotes have changed to double-quotes to allow for the interpolation. From one of your previous posts, it looks like you haven't learned about variable interpolation (excuse my presumptuousness if I'm mistaken :). Interpolation allows you to just type your variable names into double-quoted strings, and have Perl automatically replace the value with the variable's value. You can get a detailed (if not gentle) explanation of this feature in perlop.

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print