What causes "Failed to write result" in hashicorp/terraform?

Avoid piping fmt output through commands that exit before consuming the full stream (use a file redirect instead).

Failed to write result

Error message

Failed to write result

What it means

Thrown by processFile when none of -list, -write, -diff are set (the default stdout mode) and writing the formatted result to the output writer fails. This is a write failure on stdout or the configured output buffer.

Solutions

Avoid piping fmt output through commands that exit before consuming the full stream (use a file redirect instead).
Use -write to write results directly to files rather than stdout.
Verify the output destination is writable and has space.

Example fix

// before
$ terraform fmt - | head -1
// after
$ terraform fmt -write .

Defensive patterns

Strategy: try-catch

Try / catch

// When consuming fmt stdout in a pipeline, ignore EPIPE/broken-pipe.
out, err := cmd.Output()
if err != nil && !errors.Is(err, syscall.EPIPE) {
    return err
}

Prevention

Avoid piping fmt stdout through pagers/head that exit early.
Prefer -write for in-place formatting over stdout streaming.
Redirect to a file rather than through a consumer that may close the pipe.

When it happens

Trigger: Running `terraform fmt` (or `terraform fmt -` for stdin) where the stdout pipe is broken or closed — e.g., piping to `head` which exits early, or redirecting to a full/unwritable destination.

Common situations: Piping formatted output through a consumer that closes the pipe (head, less quitting); redirecting to a full disk; CI capturing stdout to a closed file descriptor.

Related errors

AI-assisted analysis of hashicorp/terraform@d32a084675 (2026-08-11). Data as JSON: /api/errors/017c15e7b33bc215. Report an issue: GitHub.

Appendix: source

Thrown at internal/command/fmt.go:223

			if err != nil {
				diags = diags.Append(fmt.Errorf("Failed to write %s", path))
				return diags
			}
		}
		if c.diff {
			diff, err := bytesDiff(src, result, path)
			if err != nil {
				diags = diags.Append(fmt.Errorf("Failed to generate diff for %s: %s", path, err))
				return diags
			}
			w.Write(diff)
		}
	}

	if !c.list && !c.write && !c.diff {
		_, err = w.Write(result)
		if err != nil {
			diags = diags.Append(fmt.Errorf("Failed to write result"))
		}
	}

	return diags
}

func (c *FmtCommand) processDir(path string, stdout io.Writer) tfdiags.Diagnostics {
	var diags tfdiags.Diagnostics

	log.Printf("[TRACE] terraform fmt: looking for files in %s", path)

	entries, err := os.ReadDir(path)
	if err != nil {
		switch {
		case os.IsNotExist(err):
			diags = diags.Append(fmt.Errorf("There is no configuration directory at %s", path))
		default:
			// ReadDir does not produce error messages that are end-user-appropriate,

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