my $pid = open my $fh, '-|', 'sleep 3; echo aaaa' // die $!;

##</code><code>##

$ perl -MO=Deparse -e'my $pid = open my $fh, "-|", "sleep 3; echo aaaa" // die $!;'
my $pid = open(my $fh, '-|', 'sleep 3; echo aaaa');
-e syntax OK

##</code><code>##

$ perl -MO=Deparse -e'my $pid = open( my $fh, "-|", "sleep 3; echo aaaa" ) // die $!;'
my $pid = open(my $fh, '-|', 'sleep 3; echo aaaa') // die($!);
-e syntax OK