If you want to store the username and password in the hash, too, use a hash of arrays:

my %db_conn = (
    a_manager => [ 'DBI:Oracle:host=hostname1;sid=ABCDB01;port=1300', 
+'a_manager', 'a_manager' ],
    b_manager => [ 'DBI:Oracle:host=hostname1;sid=ABCDB01;port=1300', 
+'b_manager', 'b_manager' ],
    c_manager => [ 'DBI:Oracle:host=hostname1;sid=ABCDB01;port=1300', 
+'c_manager', 'c_manager' ],
    d_manager => [ 'DBI:Oracle:host=hostname1;sid=CBADB01;port=1300', 
+'d_manager', 'd_manager' ],
);
[download]

And dereference the value in the connection call:

my $dbh = DBI->connect(@$data_source) or ...
[download]

Update: Added the example.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]