perl function msgrcv

In Perl, the msgrcv function is used to receive a message from a message queue. Here's an example that demonstrates how to use msgrcv:

#!/usr/bin/perl

use strict;
use warnings;
use IPC::SysV qw(IPC_PRIVATE S_IRUSR S_IWUSR msgget msgctl IPC_NOWAIT);
use IPC::Msg;

my $key = IPC_PRIVATE;
my $msgid;

# Create a new message queue or get the identifier of an existing message queue
$msgid = msgget($key, S_IRUSR | S_IWUSR);

# Check if the operation succeeded
if ($msgid == -1) {
    die "Failed to create message queue: $!\n";
}

# Define the message structure
my $msg = 'Hello, world!';
my $msgtype = 1;

# Send the message to the queue
$msg->snd($msgid, $msgtype);

# Receive the message from the queue
my $received = '';
my $rcv_msgtype;
my $msgsz = length($msg);

my $result = msgrcv($msgid, $received, $msgsz, $msgtype, IPC_NOWAIT);

# Check if the operation succeeded
if ($result == -1) {
    die "Failed to receive message from queue: $!\n";
}

print "Received message: $received\n";

In this example, we first create a message queue or get the identifier of an existing message queue using the msgget function, as shown in the previous example. We then define the message structure by creating a scalar variable $msg that contains the message to be sent, and an integer variable $msgtype that specifies the message type.

To send the message to the queue, we use the snd method of the IPC::Msg module, passing in the message queue identifier and the message type as arguments.

To receive the message from the queue, we use the msgrcv function, passing in the message queue identifier, a scalar variable $received to hold the received message, the size of the message $msgsz, the message type $msgtype, and the flags IPC_NOWAIT to specify that the function should not block if no message is available. If the function succeeds, it returns the length of the received message. If it fails, it returns -1.

Finally, we print the received message to the console.