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CGI::Carp(3)	      User Contributed Perl Documentation	  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

       The standard warn(), die	(), croak(), confess() and carp() calls	will
       be replaced with	functions that write 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, 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, 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 may not work well 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.

SUPPRESSING PERL ERRORS	APPEARING IN THE BROWSER WINDOW
       A problem sometimes encountered when using fatalsToBrowser is when a
       "die()" is done inside an "eval"	body or	expression.  Even though the
       fatalsToBrower support takes precautions	to avoid this, you still may
       get the error message printed to	STDOUT.	 This may have some
       undesirable effects when	the purpose of doing the eval is to determine
       which of	several	algorithms is to be used.

       By setting $CGI::Carp::TO_BROWSER to 0 you can suppress printing	the
       "die" messages but without all of the complexity	of using
       "set_die_handler".  You can localize this effect	to inside "eval"
       bodies if this is desirable: For	example:

	eval {
	  local	$CGI::Carp::TO_BROWSER = 0;
	  die "Fatal error messages not	sent browser"
	}
	# $@ will contain error	message

MAKING WARNINGS	APPEAR AS HTML COMMENTS
       It is 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

TURNING	OFF TIMESTAMPS IN MESSAGES
       If your web server automatically	adds a timestamp to each log line, you
       may not need CGI::Carp to add its own. You can disable timestamping by
       importing "noTimestamp":

	   use CGI::Carp qw(noTimestamp);

       Alternatively you can set $CGI::Carp::NO_TIMESTAMP to 1.

       Note that the name of the program is still automatically	included in
       the message.

GETTING	THE FULL PATH OF THE SCRIPT IN MESSAGES
       Set $CGI::Carp::FULL_PATH to 1.

AUTHOR INFORMATION
       The CGI.pm distribution is copyright 1995-2007, Lincoln D. Stein. It is
       distributed under the Artistic License 2.0. It is currently maintained
       by Lee Johnson with help	from many contributors.

       Address bug reports and comments	to:
       https://github.com/leejo/CGI.pm/issues

       The original bug	tracker	can be found at:
       https://rt.cpan.org/Public/Dist/Display.html?Queue=CGI.pm

       When sending bug	reports, please	provide	the version of CGI.pm, the
       version of Perl,	the name and version of	your Web server, and the name
       and version of the operating system you are using.  If the problem is
       even remotely browser dependent,	please provide information about the
       affected	browsers as well.

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

perl v5.32.1			  2020-09-25			  CGI::Carp(3)

NAME | SYNOPSIS | DESCRIPTION | REDIRECTING ERROR MESSAGES | MAKING PERL ERRORS APPEAR IN THE BROWSER WINDOW | DOING MORE THAN PRINTING A MESSAGE IN THE EVENT OF PERL ERRORS | SUPPRESSING PERL ERRORS APPEARING IN THE BROWSER WINDOW | MAKING WARNINGS APPEAR AS HTML COMMENTS | OVERRIDING THE NAME OF THE PROGRAM | TURNING OFF TIMESTAMPS IN MESSAGES | GETTING THE FULL PATH OF THE SCRIPT IN MESSAGES | AUTHOR INFORMATION | SEE ALSO

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