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gopalr has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks,

I am new to CGI. I want to know, how to debug the CGI coding. In windows we can use PerlIDE to debug the code like that I want.

Now I am using the following to debug the CGI Code. 

print STDERR $var;  #(we can show the value of $var in error_log file)
+;

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Please let me know, is there any other way to debug the CGI Code.

I am using Linux and Apacher Server.

Thanks
Gopal R.

Replies are listed 'Best First'.
Re: How to Debug the CGI Codes
by McDarren (Abbot) on Jul 10, 2006 at 06:58 UTC
    There are all sorts of methods you can employ for debugging CGI code - here are a couple that I often use: 
    use CGI::Carp qw/fatalsToBrowser/;

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    This will throw any errors or warnings to your browser. (Never leave this enabled in production code). 

    use Data::Dumper::Simple;
print q(<pre>);
print Dumper(%foo);

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    Useful for examining the contents of any data structure. 
    my @params = param();
print q(<pre>);
for (@params) {
    print "$_ :: $params[$_]\n";
}

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    Useful to find out which CGI parameters were passed and what their values are.

    Hope this helps,
    Darren :)

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      For development, I even use:

      use CGI::Carp qw/fatalsToBrowser warningsToBrowser/;

      because it also handles warnings

      Update: is wrong, see the posting from reneeb below

      Best regards,
      perl -e "s>>*F>e=>y)\*martinF)stronat)=>print,print v8.8.8.32.11.32"

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        To handle warnings, you have to call the warningsToBrowser subroutine with a true argument. See documentation of CGI::Carp.
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        Just a note:
        warningsToBrowser(1) must be explicitly called after printing the page header, and will output all warnings as HTML comments. It's its difference from fatalsToBrowser, which catches all fatal errors (even compile-time!) without any additional actions. The CGI::Carp documentation contains additional info.

        UPD: i haven't seen the previous reply while writing this :)

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Re: How to Debug the CGI Codes
by davorg (Chancellor) on Jul 10, 2006 at 07:58 UTC

    In addition to the excellent advice you've already got from McDarren it's worth pointing out that CGI::Carp is a very useful module for getting nicely formatted error messages out of a CGI program. In particular, I recommend the "carpout" function which allows you to set up an alternative log file that CGI::Carp messages get written to.

    You should also be aware that a CGI program really isn't that much different to any other Perl program and you don't need to run it on a web server. As long as the required inputs are set up, you can run a CGI program from the command line. I've debugged many a problematic CGI program using Perl's built-in debugger.

    --
    <http://dave.org.uk>

    "The first rule of Perl club is you do not talk about Perl club."
    -- Chip Salzenberg

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