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CGI::Carp(3) User Contributed Perl Documentation 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";
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 automagi-
cally 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 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(\*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).
Note that fatalsToBrowser does not work with mod_perl version 2.0 and higher.
Changing the default message
By default, the software error message is followed by a note to contact the Webmas-
ter 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 "warningsTo-
Browser" 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=\"text/javascript\"><!--\n";
print_some_javascript_code();
print "//--></script>\n";
warningsToBrowser(1); # re-enable warnings
Note: In this respect warningsToBrowser() differs fundamentally from fatalsTo-
Browser(), which you should never call yourself!
OVERRIDING THE NAME OF THE PROGRAM
CGI::Carp includes the name of the program that generated the error or warning in
the messages written to the log and the browser window. Sometimes, Perl can get
confused about what the actual name of the executed program was. In these cases,
you can override the program name that CGI::Carp will use for all messages.
The quick way to do that is to tell CGI::Carp the name of the program in its use
statement. You can do that by adding "name=cgi_carp_log_name" to your "use" state-
ment. For example:
use CGI::Carp qw(name=cgi_carp_log_name);
. If you want to change the program name partway through the program, you can use
the "set_progname()" function instead. It is not exported by default, you must
import it explicitly by saying
use CGI::Carp qw(set_progname);
Once you’ve done that, you can change the logged name of the program at any time by
calling
set_progname(new_program_name);
You can set the program back to the default by calling
set_progname(undef);
Note that this override doesn’t happen until after the program has compiled, so any
compile-time errors will still show up with the non-overridden program name
CHANGE LOG
1.29 Patch from Peter Whaite to fix the unfixable problem of CGI::Carp
not behaving correctly in an eval() context.
1.05 carpout() added and minor corrections by Marc Hedlund
<hedlund AT 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 AT cogit.com) to allow
module to run correctly under mod_perl.
1.11 Changed order of > and < 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 AT itz.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 combinations of Perl and
mod_perl.
1.24 Patch from Scott Gifford (sgifford AT suspectclass.com): Add support
for overriding program name.
1.26 Replaced CORE::GLOBAL::die with the evil $SIG{__DIE__} because the
former isn’t working in some people’s hands. There is no such thing
as reliable exception handling in Perl.
1.27 Replaced tell STDOUT with bytes=tell STDOUT.
AUTHORS
Copyright 1995-2002, Lincoln D. Stein. All rights reserved.
This library is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.
Address bug reports and comments to: lstein AT cshl.org
SEE ALSO
Carp, CGI::Base, CGI::BasePlus, CGI::Request, CGI::MiniSvr, CGI::Form,
CGI::Response
if (defined($CGI::Carp::PROGNAME))
{
$file = $CGI::Carp::PROGNAME;
}
perl v5.8.6 2001-02-03 CGI::Carp(3)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2009-01-10 08:11 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)