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 (for debugging, not for public consumption).

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.

If you want to send errors to the browser, give carpout() a reference to STDOUT:

   BEGIN {
     use CGI::Carp qw(carpout);
     carpout(STDOUT);
   }

If you do this, be sure to send a Content-Type header immediately -- perhaps even within the BEGIN block -- to prevent server errors.

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

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.

AUTHORS

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

carpout() added and minor corrections by Marc Hedlund <hedlund@best.com> on 11/26/95.

SEE ALSO

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

cpanm CGI::Base

perl -MCPAN -e shell
install CGI::Base