I think, that if you rewrite this with sysread/syswrite, or, like in merlyn's solution with length-based communication, it starts working.
in reply to Re^6: How to tell a child what to do?
in thread How to tell a child what to do?
This may have something to do with perl's buffering,
in particular, when instead of while (<>) I wrote this:
it stopped hanging on close($fd).
print "Received(child $$): $q\n";
When I traced what is happening when it hangs, it looks like parent is waiting waitpid(..) (close($fd) on pipe is supposed to do that), while child blissfully unaware is running read...
Now I can safely go and try to understand merlyn's code.