i did this in terminal:

export DBI_DSN=dbi:ODBC:<dbname>


in the perlscript i use this (works under windows):

my $myConnection = DBI->connect("dbi:ODBC:Driver={SQL Server};SERVER=<db dsn>; database=<dbname>; PORT=<xxxx>;UID=$username;PWD=$password")
or die "Error connection to databse $DBI::errstr";

if i execute it i get this:

DBI connect('Driver={SQL Server};SERVER=db dsn>; database=<dbname>; PORT=<xxxx>;UID=<user>;PWD=<pw>','',...) failed: [unixODBC][Driver Manager]Can't open lib 'SQL Server' : file not found (SQL-01000) at testperldb.pl line 10.
Error connection to databse [unixODBC][Driver Manager]Can't open lib 'SQL Server' : file not found (SQL-01000) at testperldb.pl line 10.