Hi monks,

I want to launch a programm, parse STDOUT and STDERR an react on different outputs. Unfortunately I cannot get rid of buffering. Here is a simple example

Program I want to launch:

#!/usr/bin/perl
print "Please press return\n";
my $line = <STDIN>;
print "OK, exit now\n";
[download]

Main program

#!/usr/bin/perl

use strict;
use warnings;

use IO::Handle;
use IPC::Open3;

my $fh_out = new IO::Handle;
my $fh_in  = new IO::Handle;
my $fh_err = new IO::Handle;

my $pid = open3($fh_in,$fh_out,$fh_err,'./skript_above.pl');

$fh_out->autoflush(1); #Putting these lines above open3
$fh_err->autoflush(1); #doesn't seem to work either

while (!$fh_out->eof) {
    my $line = $fh_out->getline;
    print "TIME: ".localtime()." OUTPUT: ".$line;
    if ($line =~ m/^Please press return/ ) {
        $fh_in->print("\n"); #provide the desired input
    }
}

waitpid($pid,0);
[download]

In the real program I use IO::Select to read $fh_out and $fh_err and the called program is a binary file (sqlplus)

Problem: The second script justs hangs because the output "Please press return\n" from the first script seems to be buffered. As a result the first script is already waiting for some input but never gets one.

If I change the first skript to

#!/usr/bin/perl

use IO::Handle;    #new
STDOUT->autoflush; #new

print "Please press return\n";
my $line = <STDIN>;
print "OK, exit now\n";
[download]

the second script works as aspected:

TIME: Wed Jan  6 23:03:34 2010 OUTPUT: Please press return
TIME: Wed Jan  6 23:03:34 2010 OUTPUT: exit
[download]

Now here is my question: Is there a way to prevent buffering without changing the called program? Why is $fh_out->autoflush(1) not working?

-Stefan

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