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this is warning 2 at C:\TEMP\junk2.pl line 19. In order to separate event of entering the block scope and leaving it, the debug print statements are used. Second problem: The usefulness of the error message depends to some extent on the programmer's coding style. Step #3: Run the script from the command line Trying to debug a Perl script through a web browser can be difficult. Source

Bit of a smartass, but it does copy/paste, and it does provide an example of named-ref style params :) #!/usr/bin/perl use warnings; use strict; my $need_work = 10; my $i_tried = Did you check the return value and examine $! Knowing the problem is most of the fix. Contact Us - Advertising Info - Rules - LQ Merchandise - Donations - Contributing Member - LQ Sitemap - Main Menu Linux Forum Android Forum Chrome OS Forum Search LQ http://stackoverflow.com/questions/2165022/how-can-i-troubleshoot-my-perl-cgi-script

Perl Cgi Error Log

No, the same system calls trace is printed every second. The script will be aborted before it has had a chance to close() the file, which is just as bad as if we forgot to close it. diagnostics mode adds a large performance overhead in comparison with just having warnings mode On. The label is optional - the filename of the script will be used by default.

Very easily: use Data::Dumper; print Dumper \$data; What we get is a pretty-printed $data: $VAR1 = \{ 'hash' => { 'foo' => 'oof', 'bar' => 'rab' }, 'array' => [ 'a', The documentation for your server might not be available to you if you are using a commercial product. There is more information about Apache::Status in its manpage. Cgi::carp Any other process requesting a lock on the same file (or resource) will wait indefinitely for it to become unlocked.

Forum Threads Getting link from Ezine is Good or Bad? If you have a problem when using Apache::* modules, you can make a request to the script from a browser and watch the errors and warnings as they are logged to If you open a file but don't close it, you may have file descriptor leakage. Linked 0 Using perl to learn HTML forms 0 403 forbidden error in xampp while executing perl programs in fedora 20 How do I run a Perl script from within a

flock3.pl --------- use Fcntl qw(:flock); use Symbol (); use vars qw($fh); $fh = Symbol::gensym(); open $fh, "+>>filename" or die "$!"; flock $fh, LOCK_EX; # do something close $fh; $fh is still Apache Cgi Stderr They go to STDERR. Whenever you see an error or warning in the error_log, you want to get rid of it. PerlSetVar StatusOptionsAll On This single directive will enable all of the options described below.

Apache Cgi Error Log

Another CGI debugging trick that I used before I ever heard of CGI::Carp was to use eval with the DATA and __END__ facilities on the script to catch compile-time errors: #!/usr/bin/perl For example, if you receive an "Internal Server Error", the root cause could be file permissions, a syntax error, or something else entirely. Perl Cgi Error Log Let's write a very simple module, which prints "OK" to the client's browser: package Apache::Example; use Apache::Constants; sub handler{ my $r = shift; $r->send_http_header('text/plain'); print "You are OK ", $r->get_remote_host, "\n"; Cgi Debug You shouldn't use it on production server as it adds quite a bit of overhead for each request.

does the browser stop locking - and finally displays the (complete) output of test.pl: YEAH hello 2 there CMON CMON hello 3 there YEAH STEP hello 4 there NOW STEP hello You can always pepper your code with these to help you locate the problem. If your code generates warnings, with the diagnostics pragma you will use disk space much faster. e.g.: 127.0.0.1 - - [09/Jan/2001:10:27:15 +0100] "GET /perl/stopping_detector.pl HTTP/1.0" 200 16 1 127.0.0.1 - - [09/Jan/2001:10:28:18 +0100] "GET /perl/test.pl HTTP/1.0" 200 10 - Detecting Aborted Connections Let's use the knowledge we Perl Cgi Print To Console

This happens when the server didn't get as far as opening the error_log file for writing before it needed to write an error message. While you're debugging your script, it's a good idea to get the fatal error messages to display in your browser somehow. There is a chance that the user may abort the request (for example by pressing his browser's Stop or Reload buttons) during the critical section. PerlMonks lovingly hand-crafted by Tim Vroom.

For example if you work with dbm files just like with locking it's important to flush the dbm buffers, by calling a sync() method: END{ # make sure that the DB How To Debug Perl Script In Linux asked 3 years ago viewed 2297 times active 3 years ago Related 4How to get perl stderr to httpd log file when using syslog473Why does modern Perl avoid UTF-8 by default?2CGI debug("message string" [,VERBOSE]) Records a debug message on the stack, and prints it to STDOUT (or actually $DEBUG_FH , see the GLOBAL VARIABLES section below), if the

PerlSetVar StatusLexInfo On With this option On and the B::LexInfo module installed, subroutine lexical variable information can be viewed.

In tcsh you would do something like this: % alias err "tail -f /usr/local/apache/logs/error_log" For bash users the command is: % alias err='tail -f /var/log/apache/error_log' and from now on in the We can use the hint Perl kindly gave to us to find where in the code the die() was called. On FreeBSD you would use the fstat(1) utility. Cgi Internal Server Error Latest LQ Deal: Linux Power User Bundle Blogs Recent Entries Best Entries Best Blogs Blog List Search Blogs Home Forums HCL Reviews Tutorials Articles Register Search Search Forums Advanced Search Search

How can you discover what has gone wrong? A CGI program still has access to stdin, stdout and stderr, but these files are used somewhat differently as the program isn't running on the user's console. use CGI qw(-debug) Are you using die() or warn? The solution: do not use \'s to mark lines as continued in Perl.

Let's take a little script that obviously "hangs" the server process: stopping_detector.pl -------------------- my $r = shift; $r->send_http_header('text/plain'); print "PID = $$\n"; $r->rflush; while(1){ $i++; sleep 1; } The script gets Find More Posts by david_ross Thread Tools Show Printable Version Email this Page Search this Thread Advanced Search Posting Rules You may not post new threads You may not post You’re presented with special offers and coupons based on your viewing and buying patterns. For example: % perl myscript.cgi If there is a problem then Perl will tell you about it.

Environment variables such as PATH and LD_LIBRARY_PATH are particularly troublesome. The solution is to use an END block to place the cleanup code in: END { # some code that ensures that locks are removed } When the script is aborted, Introduction to Linux - A Hands on Guide This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started Based on this error message, can you tell what files your program failed to open?

share|improve this answer edited Oct 21 at 18:56 community wiki 14 revs, 7 users 78%brian d foy 3 Don't be shy about editing my answer if you have something to Under Perl version 5.6 Symbol.pm-like functionality is a built-in feature, so you can do: open my $fh, ">/tmp/foo" or die $!; and $fh will be automatically vivified as a valid filehandle, Exported by default, or using the :STD tag. diagnostics pragma This module extends the terse diagnostics normally emitted by both the Perl compiler and the Perl interpreter, augmenting them with the more verbose and endearing descriptions found in the

Most Perl functions will tell you if they worked or not and will set $! The server encountered an internal error or misconfiguration and was unable to complete your request. Remember to preload B::TerseSize with: PerlModule B::Terse PerlSetVar StatusGraph When StatusDumper (see above) is enabled, another link "OP Tree Graph" will be present with the dump if this configuration variable is Turn on Perl's autoflush feature by setting $| to a true value.

PerlSetVar StatusPeek On With this option On and the Apache::Peek module installed, functions and variables can be viewed in Devel::Peek style. What is the correct phraseology for declaring a fuel emergency?