#!/usr/bin/perl --
use strict;
use warnings;
use Capture::Tiny qw/ capture /;
...
#~ my @cmd = ( $^X , 'foo.cgi', qw/ a=A b=B c=C/  );
my @cmd = ( $^X , 'foo.cgi', CGI->new->self_url );
my( $stdout, $stderr, $exit ) = capture {
    system { $cmd[0] } @cmd;
};;