# Worker function.
sub process_chunk {
    my ($chunk_ref) = @_;
    my $output = '';

    open my $fh, '<', $chunk_ref;
    while (<$fh>) {
        s/[[:punct:]]//g;
        s/[0-9]//g;
        s/w(as|ere)/be/gi;
        ...

        # append to output var
        $output .= $_;
    }
    close $fh;

    # Output orderly and serially.
    MCE->relay_lock;
    print $OUT_FH $output; $OUT_FH->flush;
    MCE->relay_unlock;
}