The problem is, that lighttpd buffers all output until all process terminate.

Have you tried to flush the output stream?

This should do the trick:

sub flush {

    my $fh  = select( STDOUT );
    my $hot = $|;

    $| = 1;

    print STDOUT '';

    $| = $hot;

    select( $fh );

    return;

}
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Or just

use IO::Handle;
flush STDOUT;
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flushing the output does not work...

The only thing that works is closing STDIN, STDOUT and STDERR. But then the script stops!

This is what I have:

my $q        = new CGI;
my $session  = CGI::Session->load($q);
my $tmpfile  = $q->upload('upfile');
my $filename = $q->param('upfile');
print $q->redirect('showProgress.cgi');
close STDOUT;
close STDIN;
close STDERR;

# <-- script stops here!

append_file( 'debug', "start\n" );
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