$day = "sunday";
$userId= "mary";

BEGIN  {
push (@INC, "./dir_$day");
}

...

##</code><code>##

use strict;
use warnings;

##</code><code>##

my $userId= "mary";

BEGIN  {
   my $day = "sunday";
   push (@INC, "./dir_$day");
}

...

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;

BEGIN {
   my $day    = "sunday";
   my $userId = "mary";

   push (@INC, "./dir_$day");

   eval "use module_$userId qw( ); 1" or die $@;
   *diary = \%diary::diary;
}

##</code><code>##

   eval "use module_$userId qw( %diary ); 1" or die $@;