A phantom death

[Rabenschwinge]

I have a problem with a phantom "die" statement:

Use of uninitialized value in die at ./correct-<censored>-buch.pl line 114.
Died at ./correct-<censored>-buch.pl line 114.

However, this line does not contain a 'die', even though it used to. Currently it is: $update->execute(($autor, $titel, $verlag, $jahr, $ort, $auflage, $sprache, $einband, $seiten, $format, $stichwort, $sparteName, $lfdnr, $infotext, $preis_euro, $gewicht, $isbn)) or print "Fehler beim Aktualisieren von ISBN $isbn.\n";

I have tried reproducing the problem in a mini script, leaving the parameters for the update uninitialized or using a key for $isbn that does not exist. But not of that failed let alone caused the script to exit by a triggered "die" statement.

'$update' is defined as follows:

#!/usr/bin/env perl
use strict;
use warnings;
use DBD::mysql;
(...)
my $updateStatement =
"UPDATE `<censored>_buch`
SET
        `autor` = ?,
        `titel` = ?,
        `verlag` = ?,
        `jahr` = ?,
        `ort` = ?,
        `auflage` = ?,
        `sprache` = ?,
        `einband` = ?,
        `seiten` = ?,
        `format` = ?,
        `stichwort` = ?,
        `sparteName` = ?,
        `lfdnr` = ?,
        `infotext` = ?,
        `preis_euro` = ?,
        `gewicht` = ?
WHERE
        `isbn` = ?
LIMIT 1";
(...)
my $db = DBI->connect("DBI:mysql:database=<censored>;host=localhost;po
+rt=3306", "<censored>", "<censored>");
my $update = $db->prepare($updateStatement) or die ($DBI::errstr);

[moritz]

You could try to wrap the dying statement in an eval { ... } block, and inspect $db->errstr after that. If it's a DBI error, that might contain some useful information.

[holli]

However, this line does not contain a 'die', even though it used to

Check if the file you are editing REALLY is the file you are running.

[Anonymous Monk]

maybe restart webserver

[derby]

Is the RaiseError attribute for your db handle being set somewhere?

[shmem]

To get where the die really occurs, there's Carp, specifically Carp::confess. You can set $SIG{__DIE__} = \&Carp::confess to get a stack trace, though it's not always accurate.

If this die is occurring inside DBI, a RaiseError =>1 passed to the connect() method should give you useful information.

[jakobi]

Not yet mentioned: If everything fails, there's always the lowlevel approach of using the perl -d, type s<CR>, then keep <CR> pressed: this should give you the the last few lines of code before it dies, and thus an idea what actually happens. Maybe with a suitable breakpoint to speedup reaching the problematic line. man perlrun, man perldebug. Printing the arguments of the dying function call might also help -> perldoc -m Data::Dumper once again.

Meta: shouldn't there be an existing help/faq node on basic debugging; or do we assume this to be well-known?

[jdporter]

Meta: shouldn't there be an existing help/faq node on basic debugging; or do we assume this to be well-known?

Well, Tutorials has a section Debugging and Optimization, but it doesn't have many articles. More would be appreciated!

I've updated the Tutorials Quest with this request.