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.0;
use CGI::Carp qw(cluck);
cluck "I wouldn't do that if I were you";
use CGI::Carp qw(fatalsToBrowser);
die "Fatal error messages are now sent to browser";

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 mes

sage: 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: $!0);

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
CGI::Carp::SAVEERR. Some servers, when dealing with CGI
scripts, close their connection to the browser when the
script closes STDOUT and STDERR. CGI::Carp::SAVEERR is
there 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(OG);

This looks weird to mere mortals however, so the following
syntaxes are accepted as well:

carpout(LOG);
carpout(main::LOG);
carpout(main'LOG);
carpout();
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" sub
routine:

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 redi
rected 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 "<p>Got an error: $msg</p>";

}
set_message(handle_errors);

}

In order to correctly intercept compile-time errors, you
should call set_message() from within a BEGIN{} block.

MAKING WARNINGS APPEAR AS HTML COMMENTS

It is now also possible to make non-fatal errors appear as
HTML comments embedded in the output of your program. To
enable this feature, export the new "warningsToBrowser"
subroutine. Since sending warnings to the browser before
the HTTP headers have been sent would cause an error, any
warnings are stored in an internal buffer until you call
the warningsToBrowser() subroutine with a true argument:

use CGI::Carp qw(fatalsToBrowser warningsToBrowser);
use CGI qw(:standard);
print header();
warningsToBrowser(1);

You may also give a false argument to warningsToBrowser() to prevent warnings from being sent to the browser while
you are printing some content where HTML comments are not
allowed:

warningsToBrowser(0); # disable warnings
print "<script type=
print_some_javascript_code();
print "//--></script>0;
warningsToBrowser(1); # re-enable warnings

Note: In this respect warningsToBrowser() differs funda mentally from fatalsToBrowser(), which you should never call yourself!

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 REFER ENCE 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.

1.11 Changed order of &gt; and &lt; escapes.

1.12 Changed die() on line 217 to CORE::die to avoid -w
warning.

1.13 Added cluck() to make the module orthogonal with
Carp.

More mod_perl related fixes.

1.20 Patch from Ilmari Karonen (perl@itz.pp.sci.fi):
Added

warningsToBrowser(). Replaced <CODE> tags with <PRE>

in

fatalsToBrowser() output.

1.23 ineval() now checks both $^S and inspects the message for the "eval" pattern

(hack alert!) in order to accomodate various combina

tions of Perl and

mod_perl.

AUTHORS

Copyright 1995-2002, Lincoln D. Stein. All rights
reserved.

This library is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.

Address bug reports and comments to: lstein@cshl.org

SEE ALSO

Carp, CGI::Base, CGI::BasePlus, CGI::Request, CGI::Min
iSvr, CGI::Form, CGI::Response

perl v5.8.0 2002-06-01 CGI::Carp(3)