You look to be on the right path but not knowing the format of the switchshow command nor the schema of your table, it's a bit difficult. At a high level, you might try something along the lines of:

#!/usr/bin/perl -w
use DBI;
use Net::Telnet ();
    $t = new Net::Telnet (Timeout => 10,);

$user = "admin";
$passwd = "";

$t->open("Sparta");
$t->login($user, $passwd);
    @lines = $t->cmd("switchshow");

my $dbh = DBI->connect( ... );
my $sth = $dbh->prepare( 
  q{INSERT INTO table (field_a, field_b) VALUES (?, ?)});

foreach my $line ( @lines ) {
  #$sth->execute(1, $dbh->quote($line) );
  $sth->execute( 1, $line )
}

$dbh->commit;
$dbh->disconnect;
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updated Thanks to gmax and runrig for pointing out that quote and placeholders should not be mixed.