FAQ 9.3 How can I get better error messages from a CGI program?


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This is an excerpt from the latest version perlfaq9.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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9.3: How can I get better error messages from a CGI program?

Use the "CGI::Carp" module. It replaces "warn" and "die", plus the
normal "Carp" modules "carp", "croak", and "confess" functions with more
verbose and safer versions. It still sends them to the normal server
error log.

use CGI::Carp;
warn "This is a complaint";
die "But this one is serious";

The following use of "CGI::Carp" also redirects errors to a file of your
choice, placed in a "BEGIN" block to catch compile-time warnings as
well:

BEGIN {
use CGI::Carp qw(carpout);
open(LOG, ">>/var/local/cgi-logs/mycgi-log")
or die "Unable to append to mycgi-log: $!\n";
carpout(*LOG);
}

You can even arrange for fatal errors to go back to the client browser,
which is nice for your own debugging, but might confuse the end user.

use CGI::Carp qw(fatalsToBrowser);
die "Bad error here";

Even if the error happens before you get the HTTP header out, the module
will try to take care of this to avoid the dreaded server 500 errors.
Normal warnings still go out to the server error log (or wherever you've
sent them with "carpout") with the application name and date stamp
prepended.



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