in reply to Creating a Pipe

Several issues.

  1. you are doing 2 forks.
  2. you confounded parent and child code. The child writes to, the parent reads from the pipe. 
    if ($pid = fork) { # parent
   ...
}
elsif ($pid == 0) { child
   ...
   exit;
}

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  3. don't forget to exit the child in the elsif branch to stop it executing any following code of the parent.
  4. you need a signal handler in the parent for it to get notified about the child having exited.
    Otherwise the parent will try to get a line from its pipe handle when there isn't any.

Last, you need loops in the parent and the child functions for the repeating to happen.

pipe(PIPE_READ,PIPE_WRITE);
autoflush PIPE_WRITE 1;
#my $pid = fork();
if ($pid = fork) { # parent
  $SIG{CHLD} = \&chld_handler;
  &read_pipe;         
} 
elsif (defined $pid) { # child
  &write_pipe ($pid); 
  exit;
}
else {
  die "cannot fork: $!";
}

sub chld_handler {
    warn "parent got signal @_\n";
    waitpid($pid,0);
    exit;
}

sub write_pipe {
    print "child pid $$ \n";
    while(1) {
        sleep 1;
        print "Enter message: ";
        my $usr_msg = <STDIN>;
        chomp $usr_msg;
        last unless $usr_msg;
        print "child pid = $$  message = $usr_msg\n";
        print PIPE_WRITE "$usr_msg\n";
    }
}

sub read_pipe {
    print "parent here. child pid = $pid\n";
    while ( my $msg_read = <PIPE_READ>) {
        print "received from pipe $msg_read";
    }
}

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Try to fix your program first, then read the spoiler ;-)

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

In Section Seekers of Perl Wisdom