Perl string parsing different variation - regex

Question

Experts... I'm creating another question in continuation with my earlier query.... this question is different from earlier request so I thought better to create new thread instead of confusing experts answers.
Below code connects each alias in tnsfile to the database...
1. Is there anyway I can limit each database connection only once and don't allow different alias connecting to the same database again?
I tried using hash but no able to fix this..
use strict;
use warnings;
if /^(([A-Za-z][A-Za-z0-9]*)(\.([A-Za-z][A-Za-z0-9]*))*)(\s|,|=)/
{
{
$hashref->{$1}="";
}
}
Below regex can select each SID value from file but not able to combine with if...
(/\(CONNECT_DATA\s+=\s+\(SID\s+=\s+(\w+\d+?)(\s+)?\)/)
Sample file (tnsfile.txt)
DB1.UK, DB2.UK =
(
(ADDRESS = (PROTOCAL = TCP))
(CONNECT_DATA = (SID = db1))
)
DB1.EU, DB2.CH =
(
(ADDRESS = (PROTOCAL = TCP))
(CONNECT_DATA = (SID = db1))
)
DB3.UK =
(
(ADDRESS = (PROTOCAL = TCP))
(CONNECT_DATA = (SID = db3))
)
DB3.US =
(
(ADDRESS = (PROTOCAL = TCP))
(CONNECT_DATA = (SID = db3))
)
DB4.UK.US, DB4.US =
(
(ADDRESS = (PROTOCAL = TCP))
(CONNECT_DATA = (SID = db4))
)
Expected $hashref value:
DB1.UK
DB3.UK
DB4.UK.US

Answer 1

Are you caching your database handles? It sounds like you are.
If so, you just need to create a new hash that relates SID to database handles. Then you only optionally create a new handle if that SID hasn't already been loaded.
In psuedocode:
my %dbh_by_sid;
while (<DATA>) {
my $sid = ...;
my $dbh = $dbh_by_sid{$sid} ||= DBI->connect(...)
or die "DB connect failed: $DBI::errstr";
# ...
}
This way if that particular SID has already been connected to, it will reuse the same handle.

Answer 2

This is far from a refined solution, and it breaks if the format of your tns file changes dramatically, but you could try something like this:
use strict;
my (%tns, %sid, $tns);
open IN, 'tnsfile.txt' or die;
while (<IN>) {
if (/^([\w.]+)/) {
($tns) = $1;
}
if (/SID *= *([\w.]+)/) {
$tns{$tns} = $1 unless ($sid{$1}++)
}
}
close IN;
print join "\n", keys %tns;