use strict;
use warnings;

use Fcntl      qw( SEEK_SET );
use IO::Handle qw( );

my $qfn = 'test_eagi.tmp';

open(my $fh, '+>', $qfn)
    or die("Can't create \"$qfn\": $!\n");

$fh->autoflush(1);

( my $pos = tell($fh) ) >= 0
    or die("tell: $!\n");

$fh->write('abcde')
    or die("write: $!\n");

seek($fh, $pos, SEEK_SET)
    or die("seek: $!\n");

my $buf = '';
while (!$fh->eof) {
    $fh->read($buf, 4096, length($buf))
        or die("read: $!\n");
}

print "$buf\n";
[download]

Thanks a lot for your help. Finally i solved it, mixing a little of everything. Maybe i should say before that i'm doing this in order to unit test a class wich will comunicate with Asterisk and get audio from EAGI interface wich writes the audio in fd=3.

use strict;
use warnings;

use IO::Handle;
use IO::File;

my $ftmp = new IO::File ("test_eagi.tmp",'r+');
unless ( defined $ftmp)
{
    die "Couldn't open (test_eagi.tmp)\n";
}
if ( fileno($ftmp) == 3 )
{
    print "open file with fd 3\n";
}
else
{
    die "ERROR: file opened with fd : ".fileno($ftmp)."\n";
}

$| = 1;
$ftmp->autoflush(1);

my $fh_in = new IO::Handle;
my $fh_out = new IO::Handle;
my $buff;
my $blen = 10;


$fh_out->fdopen(3,'r') || die "No se pudo abrir fh_out\n$!\n";

#$fh_out->autoflush(1);
$fh_in->autoflush(1);


my $data_a = 'a'x10;
my $data_b = 'b'x20;
print "data a: ($data_a)\n";
print "data b: ($data_b)\n";



tswrite($data_a,10);
tsread();

tswrite($data_b,20);
tsread();

tswrite($data_a,10);
tsread();
tsread();

tswrite($data_b,20);
tsread();

tsread();

$fh_out->close();
$ftmp->close();


sub tswrite
{
    my ($d,$s) = @_;

    ( my $pos = tell($ftmp) ) >= 0
        or die("tell: $!\n");

    my $r = $ftmp->write($d,$s);
    
    seek($ftmp, $pos, SEEK_SET)
        or die("seek: $!\n");
}

sub tsread
{
    $fh_out->read($buff,$blen);
    print "$buff\n";    
}
[download]