CGI::Carp(3)

NAME
CGI::Carp - CGI routines for writing to the HTTPD (or other) error log

SYNOPSIS

    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";

DESCRIPTION
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.

REDIRECTING ERROR MESSAGES
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.

MAKING PERL ERRORS APPEAR IN THE BROWSER WINDOW
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).

  Changing the default message
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.

CHANGE LOG
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.

AUTHORS
Lincoln D. Stein <lstein@genome.wi.mit.edu>. Feel free to redistribute this under the Perl Artistic License.

SEE ALSO
Carp, CGI::Base, CGI::BasePlus, CGI::Request, CGI::MiniSvr, CGI::Form, CGI::Response