Perl Cd Bookshelf [Electronic resources] نسخه متنی

19.2.1. Problem

Tracking down error messages from CGI scripts is notoriously
annoying. Even if you manage to find the server error log, you still
can't determine which message came from which script, or at what
time. Some unfriendly web servers even abort the script if it has the
audacity to emit anything out its STDERR before
the Content-Type header is generated on
STDOUT, so warnings can get you into trouble.

Enter the CGI::Carp module. It replaces warn and
die—plus the normal Carp module's
carp, croak,
cluck, 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 show up at 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 detect this and avoid the dreaded
500 Server
Error. Normal warnings still go to the server
error log (or wherever you've sent them with
carpout) with the program name and date stamp
prepended.