#!/usr/bin/perl -w

use strict;

use Socket;

sub usage
{
  die "Usage: $0 [-u uid] [-g gid] port prog-to-exec [args ...]\n";
}

# Parse Options
use vars qw(%opt);
while (@ARGV && $ARGV[0] =~ /^-([ugh])$/)
{
  shift;
  $opt{$1}=shift;
}

$opt{h} && usage();

$opt{u} = 2  # daemon
    unless $opt{u};
$opt{g} = 2  # daemon
    unless $opt{g};

# Get port and verify it
my $port = shift;
$port && $port =~ /^\d+$/
    or usage();

# Make sure there's something to exec
@ARGV >= 1
    or usage();

# We're going to give the client app the socket on STDIN, so close the
# old one...
close(STDIN);

# Create the socket and bind it to the port
socket(STDIN,PF_INET,SOCK_STREAM,getprotobyname('tcp'))
    or die "Socket error: $!";
setsockopt(STDIN,SOL_SOCKET, SO_REUSEADDR, pack("l",1))
    or die "setsockopt error: $!";
bind(STDIN,sockaddr_in($port,INADDR_ANY))
    or die "bind error: $!";

# Switch to our new user and group
$( = $) = $opt{g};
$< = $> = $opt{u};
if ($( != $opt{g} or $) != $opt{g}) { die "setgid failed\n"};
if ($> != $opt{u} or $< != $opt{u}) { die "setuid failed\n"};

# And get on with the show!
exec(@ARGV)
    or die "exec error: $!\n";
[download]

#!/usr/bin/perl -Tw

use Socket;
use strict;

listen(STDIN,SOMAXCONN)
    or die "listen error: $!\n";

for(;my $paddr=accept(CLIENT,STDIN); close(CLIENT))
{
  print CLIENT "The time is now ",scalar localtime,"\n";
}
[download]

# ~/tmp/listener -u 500 -g 500 23 ~/tmp/server