fprintf(out, " -f <string>, --result-prefix <string>\n");
fprintf(out, " for each group of identical files, write one\n");
fprintf(out, " result file whose name is the given prefix string\n");
fprintf(out, " -f <string>, --result-prefix <string>\n");
fprintf(out, " for each group of identical files, write one\n");
fprintf(out, " result file whose name is the given prefix string\n");