Why does my usage of Perl's DBI->connect fail silently?

Question

Why does this code fail silently? How do I get it to show me exactly what the SQL error is?

$dbh=DBI->connect($db_name,$db_user,$db_pass);

I modified the code to look like this:

$dbh=DBI->connect($db_name,$db_user,$db_pass)
    or die("could not connect to db: $db_name");

Which instead of allowing me to use $dbh unassigned, it will fail as expected, but it does not tell me exactly why it's failing. The values of $db_name etc, are all set with valid values as far as I can see.

I know the real error (the MySQL server is actually not running) but for future reference, I'd like to see the true error in case I am causing an auth failure for example.

Answer 1

Aha, the error is stored in $DBI::errstr, so I can modify my code like so:

$dbh=DBI->connect($db_name,$db_user,$db_pass)
    or die("could not connect to db: $DBI::errstr");

According to the documentation, it fails silently by design.

Answer 2

Pass RaiseError => 1 as an option when connecting, then your script will die on errors. My Perl shop has a standard configuration of:

{
  RaiseError => 1,
  PrintError => 0,
  AutoCommit => 1,
  mysql_auto_reconnect => 1,
}

Answer 3

Your use of 'or' is a syntax error. The listed code should not run at all.

You want:

$dbh=DBI->connect($db_name,$db_user,$db_pass) 
    or die("could not connect to db: $db_name");

Note that or die... is part of the original statement, not a new statement.

Answer 4

You're not seeing why the connect fails because you aren't doing what the DBI show you to do. The error will be in the $DBI::errstr variable:

$dbh = DBI->connect($data_source, $username, $password)
     or die $DBI::errstr;

Ensure you read the documentation for any functions or methods that you want to use. :)

Answer 5

Try including the value of $! in your die message.

$dbh = DBI->connect($db_name, $db_user, $db_pass)
  or die("could not connect to db ($db_name): $!");

See $! in perldoc perlvar.

Answer 6

Here's my usage of rjh's answer. I think I prefer this over the die approach, but not sure yet...

$dbh = DBI->connect($data_source, $username, $password, { RaiseError => 1 });