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CGI::Carp

Section: Perl Programmers Reference Guide (3)
Updated: perl 5.004, patch 04
Index

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";

DESCRIPTION

CGI scripts have a nasty habit of leaving warning messages in the errorlogs that are neither time stamped nor fully identified. Tracking downthe script that caused the error is a pain. This fixes that. Replacethe usual

    use Carp;

with

    use CGI::Carp

And the standard warn(), die (), croak(), confess() and carp() callswill automagically be replaced with functions that write out nicelytime-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 serversdirect STDERR to the server's error log. Some applications may wishto keep private error logs, distinct from the server's error log, orthey may wish to direct error messages to STDOUT so that the browserwill receive them.

The carpout() function is provided for this purpose. Sincecarpout() is not exported by default, you must import it explicitly bysaying

   use CGI::Carp qw(carpout);

The carpout() function requires one argument, which should be areference to an open filehandle for writing errors. It should becalled in a BEGIN block at the top of the CGI application so thatcompiler 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 SAVEERR. Someservers, when dealing with CGI scripts, close their connection to thebrowser when the script closes STDOUT and STDERR. SAVEERR is used toprevent 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 areaccepted as well:

    carpout(LOG);    carpout(main::LOG);    carpout(main'LOG);    carpout(\LOG);    carpout(\'main::LOG');

    ... and so on

Use of carpout() is not great for performance, so it is recommendedfor debugging purposes or for moderate-use applications. A futureversion of this module may delay redirecting STDERR until one of theCGI::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::Carparranges to send a minimal HTTP header to the browser so that even errors thatoccur in the early compile phase will be seen.Nonfatal errors will still be directed to the log file only (unless redirectedwith carpout).

CHANGE LOG

1.05 carpout() added and minor corrections by Marc Hedlund
<hedlundAATTbest.com> on 11/26/95.

1.06 fatalsToBrowser() no longer aborts for fatal errors within
eval() statements.

AUTHORS

Lincoln D. Stein <lsteinAATTgenome.wi.mit.edu>. Feel free to redistributethis under the Perl Artistic License.

Index

NAME
SYNOPSIS
DESCRIPTION
REDIRECTING ERROR MESSAGES
MAKING PERL ERRORS APPEAR IN THE BROWSER WINDOW
CHANGE LOG
AUTHORS
SEE ALSO

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