$ mysql -u plankton -p --socket=/somewhere/mysql/mysql.sock 

##</code><code>##

#perl -w
...
my %attr = ( socket => '/somewhere/mysql/mysql.sock' );
my $dbh = DBI->connect( "dbi:mysql:$db:$server", $user, $pw, \%attr );
...

##</code><code>##

DBI connect( 'blah:localhost', 'blah', ... ) failed: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' ...