I generally wrap all DBI-related procedures in eval blocks. This includes statement prepares & executes. Here's an example for DBI connections:

my $dbh;
eval {
  $dbh = DBI->connect($dsn, $stuff, { RaiseError => 1 });
  # will die if it doesn't work
}
if ($@) {
  # you can process the error string in $@ and clean it up 
  # for output
  print $error;
}
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Of course, if you connect to the DB with RaiseError set, you will have to wrap all DB-related methods in eval blocks to avoid die'ing.

Also, your code has if (undef $dbh) to check for connection errors. Yikes! This will set the value of $dbh to undef each time, and will always return undef, so the top part of your if-statement will never be executed, only the else-block. This may be why you're having problems. You probably meant to say if (not defined $dbh).

blokhead