Basically, this only means that you show some extra discipline concerning global variables, proper namespacing and such. Using a framework like CGI::Application takes you a long way here.

This way, you can have the extreme availability and ease-of-installation of pure CGI and if your site gets popular enough for performance issues to come into play, you can switch over to mod_perl. The code will continue to work (and be much faster, mainly due to eliminated startup time)

Making extensive use of mod_perl specific features (that would tie you into this architecture) is probably a lot of fun, but I do not think it is really worth the loss of flexibility.

Personally, I've only used CGI for my web development. My understanding is that mod_perl is better suited for larger sites with higher bandwidths because it not interpreted as straight CGI is (I'm sure I'll get some interesting replies and -- for that lame explanation). It runs faster and leaner as a result.

If you are just beginning, you might want to get your feet wet with straight Perl and CGI (be sure to take Ovid's classic course). You'll learn the basics, most of which can be applied to mod_perl once you make the switch.

I highly recommend you adapt a templating system early on. I use HTML::Template which is widely supported here at the Monastery. Also consider CGI::Application which will force you to write more structured code, and will lighten some of the coding burden.

++ Catalyst is the best :)

I server quite a few CGI scripts from a fairly slow server, and the problem is that although perl scripts will run very fast, it's very slow to create new processes, initialise perl, and load all the modules before my script starts its work.

mod_perl solves this one by having all the modules loaded in advanced, and it's registry modules can cache compiled scripts in memory. But it's rather complicated, and your memory usage can get out of hand if you aren't watching, so I tried FastCGI. It's much simpler.

Rather than loading the script into apache, it creates a process for the script a lot like CGI, but it then just keeps on reusing it rather than discarding it after one use. The other advantage is that using CGI::Fast it's easy to convert your CGI scripts to FastCGI.

So my suggestion is that if you're starting out with Perl is to go with CGI since it's simpler, and you do have room to expand to mod_perl or FastCGI later.

--
integral, resident of freenode's #perl

A good question, but, at least partly, the wrong question. CGI is a useful low-level suite of tools for emitting HTML. It will happily emit HTML to a file, to a screen, or to a web server. Apache will display the output from programs written with CGI, but you need a perl interpreter, either your normal one (/usr/bin/perl or whatever), or one built into Apache.

mod_perl is a very different animal, it is, specifically, a perl interpreter embedded into the Apache webserver. As such it doesn't do anything unless and until you feed it.

CGI is quite a good choice for feeding mod_perl, athough not the only one. It is also easy to learn, and once you understand how CGI works, learning other frameworks will be significantly easier. mod_perl can do stuff that CGI can't, but you won't get near that stuff to start with.

My own 2 cents - start with CGI and the perl interpreter on your system if you're using Linux. In Windows go with mod_perl from day 1, only because it's a bit easier to setup. If your Apache has mod_perl set up, use it. You normally only need mod_perl if your site gets very popular.

Have fun, and a Happy Christmas to all

...and I'll add my two cents. Do you manage the web server you'll be using? If not, mod_perl might be out of the question, since it's part of the web server.

You can use the CGI module without having total control of the web server, so my vote says concentrate on that.

Also, while mod_perl will make your code faster in a few situations, CGI.pm will make your code better in almost all situations. Go play with CGI.pm.

Performance is cool, but good code is cooler.

-Pileofrogs

Note that using cgi is not the same as using the CGI.pm module. The main difference between cgi and mod_perl is that for mod_perl the perl interpreter is embedded in the Apache process.

When writing/testing a web application, one advantage of cgi over mod_perl is that because cgi reloads your modules for each request, you can easily make changes without having to restart the server. mod_perl does have some tricks to get around that though.

The CGI.pm module helps make using cgi on a server easier, it can parse POST parameters, bake cookies, and generate compliant HTML code. With mod_perl some of that functionality is provided by the Apache:: modules, but you can use some parts of CGI.pm in mod_perl as well. So by all means, whether you use cgi or mod_perl, you should learn how to work with CGI.pm.

# here is the web page.
package WebPageOne;

sub new
{
    bless {}, shifth;
}

sub html
{
print <<EOP;
<head>
<body>
This is a web page.
</body>
</head>
}
1;
[download]

#!/usr/bin/perl
# webpageone.cgi

use WebPageOne;

print "content-type: text/html\n\n";

my $x = WebPageOne->new()

print $x->html;
[download]

package ModPerlPageOne;

use Apache2::Const -compile => qw(OK);

sub handler
{
    my $r = shift;
    my $x = WebPageOne->new();

    $r->send_http_header('text/html');
    
    $r->print $x->html;

    return OK;
}
[download]

No matter what your server load, cgi scripts can be a little sluggish IMHO, especially if they start opening up database connections and the like. If your traffic is low, your server will surely survive, but your users won't be impressed.

You can also run PHP as CGI, and I wouldn't be so sure that CGI PHP runs more efficiently than CGI Perl. Basicaly any mod_something is more efficient than CGI something. Also I'm not so sure which one is easier to learn, but this is probably a question of preferences.
--
Someday, people who know how to use computers will rule over those who don't. And there will be a special name for them: secretaries. -Dilbert quote

"since PHP ... runs more efficiently than CGI"

Is that true? I did some test to sort 1 million numbers and Perl runs much faster than PHP. However, the PHP zealots said that's because Perl is optimized for loop code and PHP is not good at that. They also said that PHP is more effecient to generate web pages.

Another question is that, I just thought PHP as a programming language like Perl. But CGI itself is not a language, so we can't compare PHP with CGI IMHO.