CGI::Carp(3p) Perl Programmers Reference Guide CGI::Carp(3p)
CGI::Carp - CGI routines for writing to the HTTPD (or other)
error log
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";
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.
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
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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. Exam-
ple:
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.
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If you want to send fatal (die, confess) errors to the
browser, ask to import the special "fatalsToBrowser" subrou-
tine:
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 car-
pout).
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.
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" sub-
routine. Since sending warnings to the browser before the
HTTP headers have been sent would cause an error, any warn-
ings are stored in an internal buffer until you call the
warningsToBrowser() subroutine with a true argument:
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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 fundamen-
tally from fatalsToBrowser(), which you should never call
yourself!
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 exam-
ple:
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);
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Note that this override doesn't happen until after the pro-
gram has compiled, so any compile-time errors will still
show up with the non-overridden program name
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.
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@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.
1.24 Patch from Scott Gifford (sgifford@suspectclass.com):
Add support
for overriding program name.
1.26 Replaced CORE::GLOBAL::die with the evil $SIG{__DIE__}
because the
former isn't working in some people's hands. There is
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no such thing
as reliable exception handling in Perl.
1.27 Replaced tell STDOUT with bytes=tell STDOUT.
Copyright 1995-2002, Lincoln D. Stein. All rights reserved.
This library is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.
Address bug reports and comments to: lstein@cshl.org
Carp, CGI::Base, CGI::BasePlus, CGI::Request, CGI::MiniSvr,
CGI::Form, CGI::Response
if (defined($CGI::Carp::PROGNAME))
{
$file = $CGI::Carp::PROGNAME;
}
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