Here is an example set of scripts that may show you whats up, I hope they help. :-)

#!/usr/bin/perl
# this is the init script
use warnings;
use strict;
use IPC::SysV qw(IPC_STAT IPC_PRIVATE IPC_CREAT IPC_EXCL S_IRUSR S_IWU
+SR IPC_RMID S_IRWXU);
use IPC::Msg;

# see "perldoc perlfunc /shmget" and "perldoc perlipc /SysV"
# big difference from c is attach and detach is automatic in Perl
# it attaches to read or write, then detaches

my $IPC_KEY = 1234;
my $msg = new IPC::Msg($IPC_KEY, S_IRWXU | IPC_CREAT);

my $go = 1;
$SIG{INT} = sub{ $go = 0; 
                &close_m();   #close up the shared mem
            exit;
        };

my $segment_hbytes = 0x640;   # hex bytes, a multiple of 4k
 my ($segment_id, $segment_size) = &init_m($segment_hbytes);
print "shmid-> $segment_id\tsize-> $segment_size\n";

# put the shmid on the message queue
# 1 message for each client to connect
# since each read shifts one off
my $msgout = $segment_id;

my $numclients = 3;

for(1..$numclients){
 $msg->snd(1, $msgout, 0 );
}

#check it ( will reduce the number of msgs available
#my $msgin = '';
#$msg->rcv($msgin, 8 ,0); # 8 bytes for a Perl integer
#print "msgin->$msgin\n";

#$msg->rcv($msgin, 8 ,0); # 8 bytes for a Perl integer
#print "msgin1->$msgin\n";

my $i = 'a';
while($go){ 
          &write_m($i); 
          $i++; 
      select(undef,undef,undef,.1);
          last if ! $go;
    }

exit;

#################################################################
sub init_m(){
 
 my $segment_hbytes = shift;
 
# Allocate a shared memory segment. 
  my $segment_id = shmget (IPC_PRIVATE, $segment_hbytes,
               IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR);

# Verify the segment's size.
  my $shmbuffer = '';
  shmctl ($segment_id, IPC_STAT, $shmbuffer);
  my @mdata = unpack("i*",$shmbuffer); 
return($segment_id, $mdata[9] );
}


sub write_m() {    
   # Write a string to the shared memory segment.
   my $message = shift;
   shmwrite($segment_id, $message, 0, $segment_size) || die "$!";
   return 0;
  }


sub close_m(){
 # Deallocate the shared memory segment.
  shmctl ($segment_id, IPC_RMID, 0);
  $msg->remove;
  return 0;
}
__END__
[download]

####### and this is the listener ##########################

#!/usr/bin/perl
# this script will take data from shmem
use warnings;
use strict;
use IPC::SysV qw(IPC_STAT IPC_NOWAIT);
use IPC::Msg;

#see "perldoc perlfunc /shmget" and "perldoc perlipc /SysV" 

my $IPC_KEY = 1234;
my $msg = new IPC::Msg($IPC_KEY,0);
#my $msg = new IPC::Msg($IPC_KEY, 1);

print "msg->$msg\n";

my $go = 1;

#get shmid from msg 
my $segment_id;
$msg->rcv($segment_id, 8 , 0); # 8 bytes for a Perl integer 
print "shmid->$segment_id\n"; 

$SIG{INT} = sub{ $go = 0; exit;};
                          
my $segment_size = &size_m($segment_id);
print "segment_size = $segment_size\n";

while($go){
my $readm = &read_m();
print "$readm\n";
last if ! $go;
select(undef,undef,undef,.1);
}
#############################################################

sub size_m(){
  my $segment_id = shift;
  my $shmbuffer = '';
  shmctl ($segment_id, IPC_STAT, $shmbuffer);
  my @mdata = unpack("i*",$shmbuffer);  #not sure if that is right unp
+ack? works :-) 
  print "segment size: ", $mdata[9], "\n";
  return($mdata[9]);
}

#################################################################3

sub read_m(){
   my $buff;
   #the $buff is paaded with nulls \0 to fill it out
   shmread($segment_id, $buff, 0, $segment_size) || die "$!";
   # the buffer of shmread is zero-character end-padded.
   #substr($buff, index($buff, "\0")) = '';
  return ($buff); 
}
__END__
[download]