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CGI::Carp(3pm)         Perl Programmers Reference Guide         CGI::Carp(3pm)

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

          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.  Also, note that carpout() does not work with in-memory file
       handles, although a patch would be welcome to address that.

       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 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();".

           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

       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
            <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 &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 accommodate various combinations 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 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@cshl.org

SEE ALSO
       Carp, CGI::Base, CGI::BasePlus, CGI::Request, CGI::MiniSvr, CGI::Form,
       CGI::Response

perl v5.12.1                      2010-05-07                    CGI::Carp(3pm)
 

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