Perl select return “bad file descriptor” error

Question

I am trying to implement inter process communication using pipes and the select command. Here is a first try:

use warnings;
use strict;
use feature          


        

Answer 1

  $fh->close();
  $sel->remove($fh);

You must first remove the file descriptor from the select and then close it. Once it is closed it is no longer valid (that is fileno($fh) will return undef) and cannot be removed. And if cannot be removed select will still try to select on this (invalid) file descriptor, causing EBADF.