# Process file(s).
my $status = 0;

while (my $infile = shift @ARGV) {
    if (-d $infile) {
        warn "WARN: '$infile': Is a directory, skipped\n";
        $status = 1;
    }
    elsif (! -f  $infile) {
        warn "WARN: '$infile': No such file, skipped\n";
        $status = 1;
    }
    else {
        my $outfile = $infile; $outfile =~ s/\.txt$/.dat/;
        if ($outfile eq $infile) {
            warn "WARN: '$outfile': matches input name, skipped\n";
            $status = 1;
            next;
        }
        # truncate output file
        open my $fh, '>', $outfile or do {
            warn "WARN: '$outfile': $!, skipped\n";
            $status = 1;
            next;
        };
        close $fh;
        # process file; pass argument(s) to workers
        $mce->process($infile, { user_args => [ $outfile ] });
    }
}

$mce->shutdown; # reap workers
exit $status;