A client process "C" connects to port 9876.
Inetd accepts the connection, forks, then execs() your perl program "P".
Your perl program starts a remsh process "S" which connects to a remote host and process "R".

The process P is running this code:

open(RCMD, "remsh $h -l $u $script |") || die $!;
while (<RCMD>)
{
    print $_;
}
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I think what you are asking is how your Perl program P can detect if the client C exits (or otherwises closes the socket connection). Right now it may wait a long time on <RCMD> and not give an error until the "print $_".

If this is a correct understanding, then what I suggested above should work. The STDIN and STDOUT of your Perl process P are both connected to the socket connection that "C" connected to and inetd accepted. A call to select() or can_read() should detect when that socket connection is closed.

Thank you very much for your pointers. The problem was solved by following your suggestions. The new code looks like:

   while (! eof(RCMD))
   {
      my @fds = $sel->can_read(5);
      #print NSY "FDS = @fds\n";
      if ($#fds == 0)
      {
         my $in = <RCMD>;
         print $in;
      }
      else
      {
         my @fds = $wsel->can_read(0);
         #print NSY "FDS = @fds\n";
         if ($#fds != 0)
         {
            #print NSY "Closing as stdout closed\n";
            exit(0);
         }
      }
   }
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