Thanks for the explanation. What if I fork, and have the child process feed data to the parent? That way the parent can read from the pipe when it needs to, and the child can fill it independently of the parent. Here's the modified code:

use FileHandle;

sub pipe_from_fork ($) {
   my $parent = shift;
   pipe $parent, my $child or die;
   my $pid = fork();
   die "fork() failed: $!" unless defined $pid;
   if ($pid) {
       close $child;
   }
   else {
       close $parent;
       open(STDOUT, ">&=" . fileno($child)) or die;
   }
   $pid;
}

sub decompress_filehandle
{
  my $fh = shift;

  my $dfh = new FileHandle;

  # Must use pipe_from_fork because $dfh->open('-|') not yet implement
+ed on
  # Windows. See perlfork for details
  unless (pipe_from_fork($dfh)) {
    # In child
    close $dfh;

    open(FRONT_OF_PIPE, '| c:\progra~1\cygwin\bin\gzip.exe -cd')
      or return (undef,"Can't execute \"$filter_command\" on file hand
+le: $!");

    print FRONT_OF_PIPE <$fh>;

    $fh->close()
      or return (undef,"Can't execute \"$filter_command\" on file hand
+le: $!");

    close FRONT_OF_PIPE;

    exit;
  }

  # In parent
  close $fh;
  return $dfh;
}

my $fh = new FileHandle('mailarc-1.txt.gz');
my $dfh = decompress_filehandle($fh);

print $_ while <$dfh>;
[download]

As before, this works on Unix but not Windows. It seems to hang trying to close the pipe to gzip -cd. I would have thought that this would be a common thing to do, even on Windows...

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