Ever heard of inetd? Or NPH CGI? It is quite easy to pass an open socket to a child process.

The way to do that with system (avoids fork amd exec and so is more portable) is simply to dup the socket to be STDIN and/or STDOUT (file descriptors 0 and/or 1, since file handles don't get inherited).

Use the sample code in open if you want to save then restore your existing STDIN/STDOUT, then just do:

# (save STDIN/STDOUT here)
open STDIN, "<&".fileno(*SOCK)
    or  die "Can't dup SOCK to STDIN: $!$/";
open STDOUT, ">&".fileno(*SOCK)
    or  die "Can't dup SOCK to STDOUT: $!$/";
system( ... )
   and  ...;
# (restore STDIN/STDOUT here)
[download]

Perl is smart enough to ensure that STDIN remains fd 0 and STDOUT remains fd 1 for the above.