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



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 func-
       tions 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.

       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).

       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() rou-
       tine.  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.

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 pro-
       gram.  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 pro-
       gram 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()" func-
       tion 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
       1.05 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.

       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 &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 (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 accomodate 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, CGI::MiniSvr, CGI::Form, CGI::Response
           if (defined($CGI::Carp::PROGNAME))
           {
             $file = $CGI::Carp::PROGNAME;
           }



perl v5.8.8                       2001-09-21                      CGI::Carp(3)