


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




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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:




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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();".








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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



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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
            <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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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 (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,



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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;
           }




















































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