nodejs/node · error

write to standard output already set (-o)\n

Error message

write to standard output already set (-o)\n

What it means

The `-o PATH` option sets the single output destination (`params->output_path`) and is latched by `output_set`. A second `-o` would leave the destination ambiguous, so brotli rejects it with COMMAND_INVALID. Note `-o` writes to a file path; do not confuse it with stdout (`-c`).

Source

Thrown at deps/brotli/c/tools/brotli.c:449

        /* o/q/w/C/D/S with parameter is expected */
        if (c != 'o' && c != 'q' && c != 'w' && c != 'C' && c != 'D' &&
            c != 'S') {
          fprintf(stderr, "invalid argument -%c\n", c);
          return COMMAND_INVALID;
        }
        if (j + 1 != arg_len) {
          fprintf(stderr, "expected parameter for argument -%c\n", c);
          return COMMAND_INVALID;
        }
        i++;
        if (i == argc || !argv[i] || argv[i][0] == 0) {
          fprintf(stderr, "expected parameter for argument -%c\n", c);
          return COMMAND_INVALID;
        }
        params->not_input_indices[next_option_index++] = i;
        if (c == 'o') {
          if (output_set) {
            fprintf(stderr, "write to standard output already set (-o)\n");
            return COMMAND_INVALID;
          }
          params->output_path = argv[i];
        } else if (c == 'q') {
          if (quality_set) {
            fprintf(stderr, "quality already set\n");
            return COMMAND_INVALID;
          }
          quality_set = ParseInt(argv[i], BROTLI_MIN_QUALITY,
                                 BROTLI_MAX_QUALITY, &params->quality);
          if (!quality_set) {
            fprintf(stderr, "error parsing quality value [%s]\n", argv[i]);
            return COMMAND_INVALID;
          }
        } else if (c == 'w') {
          if (lgwin_set) {
            fprintf(stderr, "lgwin parameter already set\n");
            return COMMAND_INVALID;

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Keep exactly one `-o PATH`; remove the duplicate.
2. For multiple inputs use output naming via suffix (`-S`) rather than `-o`.
3. Strip any `-o` injected by aliases/functions before adding a user one.

Example fix

# before
brotli -o a -o b in
# after
brotli -o b in

# bash: at most one -o / --output
o=$(printf '%s\n' "$@" | grep -cE '^(-o|--output.*)$')
if [ "$o" -gt 1 ]; then echo "multiple output paths" >&2; exit 2; fi
brotli "$@"

# bash
if ! brotli "$@"; then rc=$?; echo "brotli exit $rc; check -o duplicates" >&2; exit "$rc"; fi

When it happens

Trigger: `brotli -o a -o b in`, or a wrapper plus a user both adding `-o`.

Common situations: Generated pipelines concatenating flag lists; an alias `brotli='brotli -o /tmp/out'` colliding with an explicit user `-o`.

Related errors

• write to standard output already set\n
• write to standard output already set
• argument -K / --concatenated already set\n
• quality already set\n
• lgwin parameter already set\n

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/c99f13bdcf5fd7ec. Report an issue: GitHub.