What causes "write to standard output already set (--output)\n" in nodejs/node?

Choose one destination: either `--output=PATH` or `--stdout`/`-c`, not both.

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

Error message

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

What it means

The `--output=PATH` long option shares the `output_set` flag with `--stdout`/`-c`. Specifying `--output=` when `--stdout` (or another `--output=`) was already set returns COMMAND_INVALID, because the two output destinations are mutually exclusive. The dedicated message adds `(--output)` to disambiguate from the bare `--stdout` duplicate error.

Source

Thrown at deps/brotli/c/tools/brotli.c:655

          if (lgwin_set) {
            fprintf(stderr, "lgwin parameter already set\n");
            return COMMAND_INVALID;
          }
          lgwin_set = ParseInt(value, 0,
                               BROTLI_LARGE_MAX_WINDOW_BITS, &params->lgwin);
          if (!lgwin_set) {
            fprintf(stderr, "error parsing lgwin value [%s]\n", value);
            return COMMAND_INVALID;
          }
          if (params->lgwin != 0 && params->lgwin < BROTLI_MIN_WINDOW_BITS) {
            fprintf(stderr,
                    "lgwin parameter (%d) smaller than the minimum (%d)\n",
                    params->lgwin, BROTLI_MIN_WINDOW_BITS);
            return COMMAND_INVALID;
          }
        } else if (strncmp("output", arg, key_len) == 0) {
          if (output_set) {
            fprintf(stderr,
                    "write to standard output already set (--output)\n");
            return COMMAND_INVALID;
          }
          params->output_path = value;
        } else if (strncmp("quality", arg, key_len) == 0) {
          if (quality_set) {
            fprintf(stderr, "quality already set\n");
            return COMMAND_INVALID;
          }
          quality_set = ParseInt(value, BROTLI_MIN_QUALITY,
                                 BROTLI_MAX_QUALITY, &params->quality);
          if (!quality_set) {
            fprintf(stderr, "error parsing quality value [%s]\n", value);
            return COMMAND_INVALID;
          }
        } else if (strncmp("suffix", arg, key_len) == 0) {
          if (suffix_set) {
            fprintf(stderr, "suffix already set\n");

View on GitHub (pinned to 1b2de5e052)

Solutions

Choose one destination: either `--output=PATH` or `--stdout`/`-c`, not both.
Inspect aliases and `BROTLI_OPTS` for hidden `-c`.
If using `--output=`, remove any prior `-c`/`--stdout` and any prior `--output=`.

Example fix

# before
brotli -c --output=out.br input.txt
# after
brotli --output=out.br input.txt

Defensive patterns

Strategy: validation

Validate before calling

# Enforce mutual exclusion of --output= with --stdout/-c and itself.
count=0
for a in "$@"; do
  case "$a" in
    --output=*) count=$((count+1));;
    --stdout|-c) count=$((count+1));;
  esac
done
[ "$count" -gt 1 ] && { echo 'output destination conflict' >&2; exit 2; }

Prevention

Decide output destination (file vs stdout) once, before constructing the command.
Avoid `alias brotli='brotli -c'`; if you must, never combine with `--output=`.
Remember also that `--output=` cannot be used with multiple input files (later parser check).

When it happens

Trigger: Invoking `brotli -c --output=out file`, `brotli --stdout --output=out file`, or `--output=a --output=b`.

Common situations: Aliases that default to `-c` (stdout) colliding with explicit `--output=`; CI scripts that pipe to stdout for logging while a build step sets an output file; copy-paste assembling two snippets.

Related errors

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/630d48eb17739143. Report an issue: GitHub.