MirOS Manual: CGI::Carp(3p)


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

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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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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" 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.

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" 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!

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 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

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.

     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 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.

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
         if (defined($CGI::Carp::PROGNAME))
         {
           $file = $CGI::Carp::PROGNAME;
         }

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