# non-blocking pipe using O_NONBLOCK file flag, unsafe(?)

  ...
  open $in, '-|', $command or die $!;
# modified by bliako to set the filehandle to non-block IO
use Fcntl;
# EDIT: commented below is not supported and outputs warning about ORing non-numerical flags
#my $flags = "";
#fcntl($in, F_GETFL, $flags) or die "failed to get flags, $!";
# use this instead:
my $flags = fcntl($in, F_GETFL, 0);
# reporting weird flags (linux)!
print "FLAGS: '$flags'\n";
$flags |= O_NONBLOCK;
fcntl($in, F_SETFL, $flags) or die "Couldn't set file flags: $!\n";
...
# and now read is non-block,
# undef will be returned if no output ready
read $in, my $buff, 100;
if ($buff && length $buff) { # check if undef
  ...
}
...