CGI::Carp(3) 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";
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 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:
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CGI::Carp(3) CGI::Carp(3)
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. Some servers,
when dealing with CGI scripts, close their connection to the browser when
the script closes STDOUT and STDERR. SAVEERR is used 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
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).
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CGI::Carp(3) CGI::Carp(3)
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.
AUTHORS
Lincoln D. Stein <lstein@genome.wi.mit.edu>. Feel free to redistribute
this under the Perl Artistic License.
SEE ALSO
Carp, CGI::Base, CGI::BasePlus, CGI::Request, CGI::MiniSvr, CGI::Form,
CGI::Response
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