#!/usr/bin/perl -w
use strict;
use IPC::Open2;
use IO::Select;
$| = 1; # autoflush STDOUT

# Declare filehandles and command to use:
my ($r, $w);
my $cmd = 'ping 127.0.0.1';

# Open the process and set the selector:
my $pid = open2($r, $w, $cmd);
my $selector = IO::Select->new($r);

while (1)  # infinite loop (use "last" to break out)
{
if ($selector->can_read(0))
{
my $chars;
my $bytes_read = sysread($r, $chars, 4046);
print "$bytes_read $chars\n";
}

# Do anything you want in between reads here...
}

__END__

#by J. Romano

# The advantage to this script is that, if your commands (like
# "whois", "dig", and "ping") happen to pause, the loop won't
# automatically break out.  The disadvantage to this script is that it
# might be difficult figuring out when a command has finished, or just
# has delayed output (in which case you might have to put in a few
# sleep() calls).  Either way, I think that this script here does a
# better job of helping you visualize what is going on -- you just nee
+d
# to be mindful of the fact that some programs don't flush their outpu
+t
# right away, and that it's not a simple matter to tell if the program
# has stopped running altogether.
[download]

Hi,

it is not a direct answer to your question and I don't know whether your code is just an excerpt from a bigger context. But if you just want to call rsync with grabbing the output synchronosly you could use the following:

my $rsync_base_cmd = "rsync -avm -L --exclude='S/' --include='*/' --in
+clude='*.cpp' " .
     "--include='*.hpp' --exclude='*'";
  
my $command = "$rsync_base_cmd ${login}:${remoteDirectory} $localDirec
+tory";
open my $fh, '-|', $command
    or confess("_copy_component Cannot perform rsync : $!");
my $output;
while(<$fh>) {
    $output .= $_;
}
close $fh or confess("rsync problem: $!");
[download]

Best regards
McA

P.S.: untested

Hi McA,
thanks for your reply.

Well, I do not wish to necessarily grab the output from the pipe, the statement while(<$fh>) { $output .= $_; } was a trick to delay the premature death of the pipe.
I am using open3 because the remote server prints into the stderr a welcome message, which it is automatically forwarded into the client stdout using the common pipe mechanism, while I want to get rid of it.

Kind regards,
Superfox

But... you are closing the pipe yourself before the process has a chance to terminate: the close() above the waitpid().

If you want to get rid of stderr, simply redirect it. There's no need to mess with open3().

Hi,
I tried to swap waitpid & close, it still closes the process prematurely.

Kind regards,
Superfox