sub read_available {
  my ($fh) = @_;
  my $data = '';
  while (1) {
    my $buf;
    my $nread = sysread($fh, $buf, 4096);
    if (defined $nread) {
      if ($nread == 0) {
        # End of file, so we have everything we'll ever get
        return ($data, 1);
      } else {
        $data .= $buf;
      }
    } else {
      if ($!{EWOULDBLOCK}) {
        return ($data, 0);
      } else {
        return; # Error
      }
    }
  }
}
.
.
.
# Set STDIN nonblocking
IO::Handle->new_from_fd(fileno(STDIN), "r")->blocking(0);
.
.
.
# If select says that STDIN is readable...
my ($data, $eof) = read_available(*STDIN)
  or die "Error reading stdin: $!";