CGI::Carp(3) Perl Programmers Reference Guide CGI::Carp(3)NAMECGI::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::Carpqw(cluck);
cluck "I wouldn't do that if I were you";
use CGI::Carpqw(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
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import it explicitly by saying
use CGI::Carpqw(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::Carpqw(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 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
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"
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subroutine:
use CGI::Carpqw(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).
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 "Got an error: $msg";
}
set_message(\&handle_errors);
}
In order to correctly intercept compile-time errors, you
should call set_message() from within a BEGIN{} block.
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.
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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.
AUTHORS
Copyright 1995-1998, 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::MiniSvr, CGI::Form, CGI::Response
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