$ perl -e'open my $fh, "cat |" or die $!'
<waits forever>

$ perl -e'open our $fh, "cat |" or die $!'
<returns immediately>

##</code><code>##

$ perl -e'open our $fh, "cat |" or die $!; close($fh)'
<waits forever>

##</code><code>##

$ perl -e'my $pid = open my $fh, "cat |" or die $!; kill TERM => $pid'
<returns immediately>