1CGI::Carp(3) User Contributed Perl Documentation CGI::Carp(3)
2
6 CGI::Carp - CGI routines for writing to the HTTPD (or other) error log
7
9 use CGI::Carp;
10 croak "We're outta here!";
12 confess "It was my fault: $!";
13 carp "It was your fault!";
14 warn "I'm confused";
15 die "I'm dying.\n";
16 use CGI::Carp qw(cluck);
18 cluck "I wouldn't do that if I were you";
19 use CGI::Carp qw(fatalsToBrowser);
21 die "Fatal error messages are now sent to browser";
22
24 CGI scripts have a nasty habit of leaving warning messages in the error
25 logs that are neither time stamped nor fully identified. Tracking down
26 the script that caused the error is a pain. This fixes that. Replace
27 the usual
28 use Carp;
30 with
32 use CGI::Carp
34 The standard warn(), die (), croak(), confess() and carp() calls will
36 be replaced with functions that write time-stamped messages to the HTTP
37 server error log.
38 For example:
40 [Fri Nov 17 21:40:43 1995] test.pl: I'm confused at test.pl line 3.
42 [Fri Nov 17 21:40:43 1995] test.pl: Got an error message: Permission denied.
43 [Fri Nov 17 21:40:43 1995] test.pl: I'm dying.
44
46 By default, error messages are sent to STDERR. Most HTTPD servers
47 direct STDERR to the server's error log. Some applications may wish to
48 keep private error logs, distinct from the server's error log, or they
49 may wish to direct error messages to STDOUT so that the browser will
50 receive them.
51 The "carpout()" function is provided for this purpose. Since carpout()
53 is not exported by default, you must import it explicitly by saying
54 use CGI::Carp qw(carpout);
56 The carpout() function requires one argument, a reference to an open
58 filehandle for writing errors. It should be called in a "BEGIN" block
59 at the top of the CGI application so that compiler errors will be
60 caught. Example:
61 BEGIN {
63 use CGI::Carp qw(carpout);
64 open(LOG, ">>/usr/local/cgi-logs/mycgi-log") or
65 die("Unable to open mycgi-log: $!\n");
66 carpout(LOG);
67 }
68 carpout() does not handle file locking on the log for you at this
70 point. Also, note that carpout() does not work with in-memory file
71 handles, although a patch would be welcome to address that.
72 The real STDERR is not closed -- it is moved to CGI::Carp::SAVEERR.
74 Some servers, when dealing with CGI scripts, close their connection to
75 the browser when the script closes STDOUT and STDERR.
76 CGI::Carp::SAVEERR is there to prevent this from happening prematurely.
77 You can pass filehandles to carpout() in a variety of ways. The
79 "correct" way according to Tom Christiansen is to pass a reference to a
80 filehandle GLOB:
81 carpout(\*LOG);
83 This looks weird to mere mortals however, so the following syntaxes are
85 accepted as well:
86 carpout(LOG);
88 carpout(main::LOG);
89 carpout(main'LOG);
90 carpout(\LOG);
91 carpout(\'main::LOG');
92 ... and so on
94 FileHandle and other objects work as well.
96 Use of carpout() is not great for performance, so it is recommended for
98 debugging purposes or for moderate-use applications. A future version
99 of this module may delay redirecting STDERR until one of the CGI::Carp
100 methods is called to prevent the performance hit.
101
103 If you want to send fatal (die, confess) errors to the browser, import
104 the special "fatalsToBrowser" subroutine:
105 use CGI::Carp qw(fatalsToBrowser);
107 die "Bad error here";
108 Fatal errors will now be echoed to the browser as well as to the log.
110 CGI::Carp arranges to send a minimal HTTP header to the browser so that
111 even errors that occur in the early compile phase will be seen.
112 Nonfatal errors will still be directed to the log file only (unless
113 redirected with carpout).
114 Note that fatalsToBrowser may not work well with mod_perl version 2.0
116 and higher.
117 Changing the default message
119 By default, the software error message is followed by a note to contact
120 the Webmaster by e-mail with the time and date of the error. If this
121 message is not to your liking, you can change it using the
122 set_message() routine. This is not imported by default; you should
123 import it on the use() line:
124 use CGI::Carp qw(fatalsToBrowser set_message);
126 set_message("It's not a bug, it's a feature!");
127 You may also pass in a code reference in order to create a custom error
129 message. At run time, your code will be called with the text of the
130 error message that caused the script to die. Example:
131 use CGI::Carp qw(fatalsToBrowser set_message);
133 BEGIN {
134 sub handle_errors {
135 my $msg = shift;
136 print "<h1>Oh gosh</h1>";
137 print "<p>Got an error: $msg</p>";
138 }
139 set_message(\&handle_errors);
140 }
141 In order to correctly intercept compile-time errors, you should call
143 set_message() from within a BEGIN{} block.
144
146 If fatalsToBrowser in conjunction with set_message does not provide you
147 with all of the functionality you need, you can go one step further by
148 specifying a function to be executed any time a script calls "die", has
149 a syntax error, or dies unexpectedly at runtime with a line like
150 "undef->explode();".
151 use CGI::Carp qw(set_die_handler);
153 BEGIN {
154 sub handle_errors {
155 my $msg = shift;
156 print "content-type: text/html\n\n";
157 print "<h1>Oh gosh</h1>";
158 print "<p>Got an error: $msg</p>";
159 #proceed to send an email to a system administrator,
161 #write a detailed message to the browser and/or a log,
162 #etc....
163 }
164 set_die_handler(\&handle_errors);
165 }
166 Notice that if you use set_die_handler(), you must handle sending HTML
168 headers to the browser yourself if you are printing a message.
169 If you use set_die_handler(), you will most likely interfere with the
171 behavior of fatalsToBrowser, so you must use this or that, not both.
172 Using set_die_handler() sets SIG{__DIE__} (as does fatalsToBrowser),
174 and there is only one SIG{__DIE__}. This means that if you are
175 attempting to set SIG{__DIE__} yourself, you may interfere with this
176 module's functionality, or this module may interfere with your module's
177 functionality.
178
180 A problem sometimes encountered when using fatalsToBrowser is when a
181 "die()" is done inside an "eval" body or expression. Even though the
182 fatalsToBrower support takes precautions to avoid this, you still may
183 get the error message printed to STDOUT. This may have some
184 undesirable effects when the purpose of doing the eval is to determine
185 which of several algorithms is to be used.
186 By setting $CGI::Carp::TO_BROWSER to 0 you can suppress printing the
188 "die" messages but without all of the complexity of using
189 "set_die_handler". You can localize this effect to inside "eval"
190 bodies if this is desirable: For example:
191 eval {
193 local $CGI::Carp::TO_BROWSER = 0;
194 die "Fatal error messages not sent browser"
195 }
196 # $@ will contain error message
197
199 It is also possible to make non-fatal errors appear as HTML comments
200 embedded in the output of your program. To enable this feature, export
201 the new "warningsToBrowser" subroutine. Since sending warnings to the
202 browser before the HTTP headers have been sent would cause an error,
203 any warnings are stored in an internal buffer until you call the
204 warningsToBrowser() subroutine with a true argument:
205 use CGI::Carp qw(fatalsToBrowser warningsToBrowser);
207 use CGI qw(:standard);
208 print header();
209 warningsToBrowser(1);
210 You may also give a false argument to warningsToBrowser() to prevent
212 warnings from being sent to the browser while you are printing some
213 content where HTML comments are not allowed:
214 warningsToBrowser(0); # disable warnings
216 print "<script type=\"text/javascript\"><!--\n";
217 print_some_javascript_code();
218 print "//--></script>\n";
219 warningsToBrowser(1); # re-enable warnings
220 Note: In this respect warningsToBrowser() differs fundamentally from
222 fatalsToBrowser(), which you should never call yourself!
223
225 CGI::Carp includes the name of the program that generated the error or
226 warning in the messages written to the log and the browser window.
227 Sometimes, Perl can get confused about what the actual name of the
228 executed program was. In these cases, you can override the program
229 name that CGI::Carp will use for all messages.
230 The quick way to do that is to tell CGI::Carp the name of the program
232 in its use statement. You can do that by adding
233 "name=cgi_carp_log_name" to your "use" statement. For example:
234 use CGI::Carp qw(name=cgi_carp_log_name);
236 . If you want to change the program name partway through the program,
238 you can use the "set_progname()" function instead. It is not exported
239 by default, you must import it explicitly by saying
240 use CGI::Carp qw(set_progname);
242 Once you've done that, you can change the logged name of the program at
244 any time by calling
245 set_progname(new_program_name);
247 You can set the program back to the default by calling
249 set_progname(undef);
251 Note that this override doesn't happen until after the program has
253 compiled, so any compile-time errors will still show up with the non-
254 overridden program name
255
257 If your web server automatically adds a timestamp to each log line, you
258 may not need CGI::Carp to add its own. You can disable timestamping by
259 importing "noTimestamp":
260 use CGI::Carp qw(noTimestamp);
262 Alternatively you can set $CGI::Carp::NO_TIMESTAMP to 1.
264 Note that the name of the program is still automatically included in
266 the message.
267
269 Set $CGI::Carp::FULL_PATH to 1.
270
272 The CGI.pm distribution is copyright 1995-2007, Lincoln D. Stein. It is
273 distributed under the Artistic License 2.0. It is currently maintained
274 by Lee Johnson with help from many contributors.
275 Address bug reports and comments to:
277 https://github.com/leejo/CGI.pm/issues
278 The original bug tracker can be found at:
280 https://rt.cpan.org/Public/Dist/Display.html?Queue=CGI.pm
281 When sending bug reports, please provide the version of CGI.pm, the
283 version of Perl, the name and version of your Web server, and the name
284 and version of the operating system you are using. If the problem is
285 even remotely browser dependent, please provide information about the
286 affected browsers as well.
287
289 Carp, CGI::Base, CGI::BasePlus, CGI::Request, CGI::MiniSvr, CGI::Form,
290 CGI::Response.
291perl v5.34.0 2021-07-22 CGI::Carp(3)