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RedHat 9 (Linux i386) - man page for cgi::carp (redhat section 3pm)

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 nei-
       ther 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 file-
       handle 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 prema-
       turely.

       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() 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 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 mes-
       sages 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 state-
       ment.  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 call-
       ing

	   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 com-
       pile-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 combinations of Perl and
	    mod_perl.

       1.24 Patch from Scott Gifford (sgifford@suspectclass.com): Add support
	    for overriding program name.

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;
	   }

perl v5.8.0				    2002-06-01				   CGI::Carp(3pm)


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