Plack Handbook - Running cgi scripts on plack

Day 9: Running CGI scripts on Plack

For the last couple of days we've been talking about how to convert existing CGI based applications to PSGI, and then run them as a PSGI application. Today we will show you the ultimate way to run any CGI scripts as a PSGI application, most of the time unmodified.

CGI::PSGI is a subclass of CGI.pm to allow you a very easy migration from CGI.pm with only a few lines of code changes to run it on PSGI environment. But what about a messy or legacy CGI script that just prints to STDOUT a lot and is not easy to fix?

CGI::Emulate::PSGI is a module to run any CGI based perl program in a PSGI environment. Whatever messy/old script that prints stuff to STDOUT or directly reads HTTP headers from %ENV would just work because that's what CGI::Emulate::PSGI tries to emulate. The original POD of CGI::Emulate::PSGI was illustrating it like:

 use CGI::Emulate::PSGI;
 CGI::Emulate::PSGI->handler(sub {
     do "/path/to/foo.cgi";
     CGI::initialize_globals() if &CGI::initialize_globals;
 });

to run existing CGI application that may or may not use CGI.pm (CGI.pm caches lots of environment variables so it needs initialize_globals() call to clear out the previous request variables).

A few days ago on my flight from San Francisco to London to attend London Perl Workshop I was hacking on something more intelligent, that is to take any CGI scripts and compiles it into a subroutine. The module is named CGI::Compile and should be best used combined with CGI::Emulate::PSGI.

 my $sub = CGI::Compile->compile("/path/to/script.cgi");
 my $app = CGI::Emulate::PSGI->handler($sub);

There's also Plack::App::CGIBin Plack application to run existing CGI scripts written in Perl as PSGI applications, suppose you have bunch of CGI scripts in /path/to/cgi-bin, you'll run the server with:

 > plackup -MPlack::App::CGIBin -e 'Plack::App::CGIBin->new(root => "/path/to/cgi-bin"))'

And that will mount the path /path/to/cgi-bin, so suppose you have foo.pl in that directory, you can access http://localhost:5000/foo.pl to run the CGI application as a PSGI over the plackup, just like the scripts running on Apache mod_perl Registry mechanism.