Re: System commands using CGI

[blue_cowdawg]

Hi, I am trying to execute system commands from CGI but it doesnt work.If I execute the same code from command line, the code works fine.

This is a very common "gotcha" that it would seem all Perl programmers and Perl programmer wannabes go through at some point in their Perl travels.

Stepping back from your original complaint for just a second let me share with you my typical approach for troubleshooting a CGI problem.

1. First off understand exactly how your web server is set up. What userid is your CGI environment running as being one of the first things I want to know about. Don't assume anything, that's bad for you, stunts your growth, curls your spine and causes you to forget to use strict; in your coding. :-) A handy piece of code that I use is as follows:

   #!/usr/bin/perl -w
   #-----------------------------------
   # Script to dump my environment to a browser from CGI. 
   # CAVEAT:  Never, ever by all that is holy leave this script in a 
   #          production environment
   
   use strict;
   use CGI qw/ :all /;
   
   my $cgi = new CGI;
   print $cgi->headers,$cgi->start_html;  # start the show;
   print hr,b("ENV Dump");
   print ul(
         map { li($ENV{$_} } keys %ENV
   );
   print hr,b("CGI Param Dump");
   print ul(
            map { li($cgi->param($_)) } $cgi->param
   );
   print $cgi->end_html;
   exit(0);
   

   This will give you an idea what you are dealing with and will be a big help in troubleshooting.
2. Find out where your server logs are and start watching them.
3. Embed some debugging statements into your code.
4. Run your code and watch all the fun

Given your original complaint I'd look at system permissions for both running the command in the first place (which is why your code will behave differently at the command line than when run from CGI). Typically CGI is run as a non-elevated user and on some *nix systems it is run as "nobody" or "nofiles" which will eliminate your ability to create/modify files.

Hope this helps you along your way.

[Anonymous Monk]

Helpful, but some syntax errors:

$cgi->headers

should be:

$cgi->header

missing closing ")":

map { li($ENV{$_} } keys %ENV

should be:

map { li($ENV{$_}) } keys %ENV