| |
man : CGI::Carp(3p)
CGI::Carp(3p) Perl Programmers Reference Guide CGI::Carp(3p)
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 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
perl v5.10.0 2008-09-30 1
CGI::Carp(3p) Perl Programmers Reference Guide CGI::Carp(3p)
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:
perl v5.10.0 2008-09-30 2
CGI::Carp(3p) Perl Programmers Reference Guide CGI::Carp(3p)
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 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.
DOING MORE THAN PRINTING A MESSAGE IN THE EVENT OF PERL ERRORS
If fatalsToBrowser in conjunction with set_message does
not provide you with all of the functionality you need,
you can go one step further by specifying a function to be
executed any time a script calls "die", has a syntax
error, or dies unexpectedly at runtime with a line like
"undef->explode();".
perl v5.10.0 2008-09-30 3
CGI::Carp(3p) Perl Programmers Reference Guide CGI::Carp(3p)
use CGI::Carp qw(set_die_handler);
BEGIN {
sub handle_errors {
my $msg = shift;
print "content-type: text/html\n\n";
print "<h1>Oh gosh</h1>";
print "<p>Got an error: $msg</p>";
#proceed to send an email to a system administrator,
#write a detailed message to the browser and/or a log,
#etc....
}
set_die_handler(\&handle_errors);
}
Notice that if you use set_die_handler(), you must handle
sending HTML headers to the browser yourself if you are
printing a message.
If you use set_die_handler(), you will most likely
interfere with the behavior of fatalsToBrowser, so you
must use this or that, not both.
Using set_die_handler() sets SIG{__DIE__} (as does
fatalsToBrowser), and there is only one SIG{__DIE__}. This
means that if you are attempting to set SIG{__DIE__}
yourself, you may interfere with this module's
functionality, or this module may interfere with your
module's functionality.
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=\"text/javascript\"><!--\n";
print_some_javascript_code();
print "//--></script>\n";
warningsToBrowser(1); # re-enable warnings
perl v5.10.0 2008-09-30 4
CGI::Carp(3p) Perl Programmers Reference Guide CGI::Carp(3p)
Note: In this respect warningsToBrowser() differs
fundamentally from fatalsToBrowser(), 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" statement.
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
<hedlundATbest.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.
perl v5.10.0 2008-09-30 5
CGI::Carp(3p) Perl Programmers Reference Guide CGI::Carp(3p)
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 (ctdeanATcogit.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 (perlATitz.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 accommodate various
combinations of Perl and
mod_perl.
1.24 Patch from Scott Gifford (sgiffordATsuspectclass.com):
Add support
for overriding program name.
1.26 Replaced CORE::GLOBAL::die with the evil
$SIG{__DIE__} because the
former isn't working in some people's hands. There
is no such thing
as reliable exception handling in Perl.
1.27 Replaced tell STDOUT with bytes=tell STDOUT.
AUTHORS
Copyright 1995-2002, Lincoln D. Stein. All rights
reserved.
This library is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.
Address bug reports and comments to: lsteinATcshl.org
SEE ALSO
Carp, CGI::Base, CGI::BasePlus, CGI::Request,
perl v5.10.0 2008-09-30 6
CGI::Carp(3p) Perl Programmers Reference Guide CGI::Carp(3p)
CGI::MiniSvr, CGI::Form, CGI::Response
if (defined($CGI::Carp::PROGNAME))
{
$file = $CGI::Carp::PROGNAME;
}
perl v5.10.0 2008-09-30 7
|
