For example, mSQL requires the hostname, database name, and potentially, the TCP/IP port number for connecting to the database server. However, Oracle may require only a single word that is an alias to a more complicated connection identifier that is stored in separate Oracle configuration files.

DBI offers two useful methods for querying which data sources are available to you for each driver you have installed on your system.

The following script lists all the drivers and data sources for each driver on your system:

#!/usr/bin/perl -w
#
# ch04/listdsns: Enumerates all data sources and all installed drivers
#
use DBI;

### Probe DBI for the installed drivers
my @drivers = DBI->available_drivers();

die "No drivers found!\n" unless @drivers; # should never happen

### Iterate through the drivers and list the data sources for each one
foreach my $driver ( @drivers ) {
    print "Driver: $driver\n";
    my @dataSources = DBI->data_sources( $driver );
    foreach my $dataSource ( @dataSources ) {
        print "\tData Source is $dataSource\n";
    }
    print "\n";
}

exit;

The output from this script on my machine looks like:

Driver: ADO

Driver: CSV
    Data source is DBI:CSV:f_dir=megaliths
    Data source is DBI:CSV:f_dir=pictish_stones

Driver: ExampleP
    Data Source is dbi:ExampleP:dir=.

Driver: File
    Data Source is DBI:File:f_dir=megaliths
    Data Source is DBI:File:f_dir=pictish_stones

Driver: ODBC

Driver: Proxy

Driver: XBase
    Data Source is dbi:XBase:.

While this may be interesting in theory, in practice you rarely need to use these methods. Most applications are written to use one data source name, either hardcoded into the application or passed in as a parameter in some way.