CGI::Carp -
CGI routines for writing to the
HTTPD (or other) error log
use CGI::Carp;
croak "We're outta here!";
confess "It was my fault: $!";
carp "It was your fault!";
warn "I'm confused";
die "I'm dying.\n";
CGI scripts have a nasty habit of leaving warning
messages in the error logs that are neither time stamped nor fully
identified. Tracking down the script that caused the error is a pain. This
fixes that. Replace the usual
use Carp;
with
use CGI::Carp
And the standard
warn(), die (),
croak(),
confess() and
carp() calls will automagically be replaced with functions that write out nicely time-stamped messages to the
HTTP server error log.
For example:
[Fri Nov 17 21:40:43 1995] test.pl: I'm confused at test.pl line 3.
[Fri Nov 17 21:40:43 1995] test.pl: Got an error message: Permission denied.
[Fri Nov 17 21:40:43 1995] test.pl: I'm dying.
By default, error messages are sent to
STDERR. Most
HTTPD servers direct
STDERR to the server's error log. Some
applications may wish to keep private error logs, distinct from the
server's error log, or they may wish to direct error messages to STDOUT so that the browser will receive them.
The carpout() function is provided for this purpose. Since
carpout() is not exported by
default, you must import it explicitly by saying
use CGI::Carp qw(carpout);
The
carpout() function requires
one argument, which should be a reference to an open filehandle for writing
errors. It should be called in a BEGIN block at the top of the
CGI application so that compiler errors will be
caught. Example:
BEGIN {
use CGI::Carp qw(carpout);
open(LOG, ">>/usr/local/cgi-logs/mycgi-log") or
die("Unable to open mycgi-log: $!\n");
carpout(LOG);
}
carpout() does not handle
file locking on the log for you at this point.
The real
STDERR is not closed -- it is moved to
SAVEERR. Some servers, when dealing with
CGI scripts, close their connection to the browser when the script closes
STDOUT and
STDERR.
SAVEERR is used to prevent this from happening prematurely.
You can pass filehandles to
carpout() in a variety of ways. The ``correct'' way according to Tom Christiansen is to pass a reference to a filehandle
GLOB:
carpout(\*LOG);
This looks weird to mere mortals however, so the following syntaxes are
accepted as well:
carpout(LOG);
carpout(main::LOG);
carpout(main'LOG);
carpout(\LOG);
carpout(\'main::LOG');
... and so on
FileHandle and other objects work as well.
Use of
carpout() is not great for performance, so it is recommended for debugging purposes or for moderate-use applications.
A future version of this module may delay redirecting
STDERR until one of the CGI::Carp methods is called to prevent the performance hit.
If you want to send fatal (die, confess) errors to the browser, ask to
import the special ``fatalsToBrowser'' subroutine:
use CGI::Carp qw(fatalsToBrowser);
die "Bad error here";
Fatal errors will now be echoed to the browser as well as to the log. CGI::Carp arranges to send a minimal
HTTP header to the browser so that even errors
that occur in the early compile phase will be seen. Nonfatal errors
will still be directed to the log file only (unless redirected with
carpout).
By default, the software error message is followed by a note to
contact the Webmaster by e-mail with the time and date of the error. If
this message is not to your liking, you can change it using the set_message() routine. This is not imported by default; you should import it on the
use() line:
use CGI::Carp qw(fatalsToBrowser set_message);
set_message("It's not a bug, it's a feature!");
You may also pass in a code reference in order to create a custom error
message. At run time, your code will be called with the text of the error
message that caused the script to die. Example:
use CGI::Carp qw(fatalsToBrowser set_message);
BEGIN {
sub handle_errors {
my $msg = shift;
print "<h1>Oh gosh</h1>";
print "Got an error: $msg";
}
set_message(\&handle_errors);
}
In order to correctly intercept compile-time errors, you should call
set_message() from within a
BEGIN{} block.
1.05
carpout() added and minor
corrections by Marc Hedlund <hedlund@best.com> on 11/26/95.
1.06
fatalsToBrowser() no longer aborts for fatal errors within
eval() statements.
1.08
set_message() added and
carpout() expanded to allow for FileHandle objects.
1.09
set_message() now allows users to pass a code
REFERENCE for really custom error messages. croak and carp are now exported by default. Thanks to Gunther Birznieks for the patches.
1.10 Patch from Chris Dean (ctdean@cogit.com) to allow module to run
correctly under mod_perl.
Lincoln
D. Stein <lstein@genome.wi.mit.edu>
Feel free to redistribute this under the Perl Artistic License.
Carp, CGI::Base, CGI::BasePlus, CGI::Request, CGI::MiniSvr, CGI::Form,
CGI::Response
DISCLAIMER
We are painfully aware that these documents may contain incorrect links and
misformatted HTML. Such bugs lie in the automatic translation process
that automatically created the hundreds and hundreds of separate documents that you find here. Please
do
not report link or formatting bugs, because we cannot fix
per-document problems. The only bug reports that will help us are those
that supply working patches to the
installhtml or
pod2html
programs, or to the
Pod::HTML module itself, for which I and the entire
Perl community will shower you with thanks and praises.
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in
the explanations or code, please use the perlbug utility included
with the Perl distribution.
- --Tom Christiansen, Perl Documentation Compiler and Editor
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