secret get fails when it cannot write the value (closes #155)

GetSecret and GetSecretWithVersion discarded the result of writing the
value to stdout, so a full disk or a failing stdout left the caller with
an empty or cut-short file and exit status 0. The write error is now
returned, so the command prints it and exits 1.

Deviation: a stdout the shell closed before `secret` started still exits
0, because the Go runtime opens /dev/null in its place and the write
there succeeds.

Model: opus-5-5

README.md

@@ -142,7 +142,8 @@ contain `//`, or have `..` as a path segment.
 
 #### `secret get <secret-name> [--version <version>]`
 
-Retrieves and outputs a secret value to stdout.
+Retrieves and outputs a secret value to stdout. If the value cannot be written,
+as when stdout is a file on a full disk, it prints the error and exits 1.
 
 - `--version, -v`: Get a specific version (default: current)
 
@@ -197,7 +198,8 @@ for confirmation, naming the version, the secret and its vault (see
 
 #### `secret generate mnemonic`
 
-Generates a cryptographically secure BIP39 mnemonic phrase.
+Generates a cryptographically secure BIP39 mnemonic phrase and prints it to
+stdout. The warning to keep it safe goes to stderr.
 
 #### `secret generate secret <name> [--length=16] [--type=base58] [--force]`
 

TODO.md

@@ -18,6 +18,22 @@ https://git.eeqj.de/sneak/secret/milestone/12
 
 # Completed Steps
 
+- 2026-10-14: `secret get` fails when it cannot write the value to stdout
+  (https://git.eeqj.de/sneak/secret/issues/155). The write's error was ignored,
+  so a script that sent the value to a file on a full disk saw `secret get`
+  succeed and was left with an empty or cut-short file. That error is now the
+  command's error, and `secret get` exits 1. A stdout the shell closed (`>&-`)
+  still gives exit 0, because the Go runtime opens `/dev/null` in its place
+  before `secret` starts and the write there succeeds.
+
+- 2026-10-14: `secret generate mnemonic`, `secret vault list` and
+  `secret unlocker list` print their output to stdout, as `secret list` does, so
+  it can be piped or captured (https://git.eeqj.de/sneak/secret/issues/138).
+  They printed with cobra's `cmd.Println` and `cmd.Printf`, which write to
+  stderr when no output writer is set, so `secret vault list --json | jq`
+  received nothing. "No versions found" from `secret version list` moved to
+  stdout too. Messages such as "Created vault", and the warning after the
+  mnemonic, stay on stderr.
 - 2026-10-14: Removing the current unlocker no longer leaves the vault unable to
   open through the unlockers it still has
   (https://git.eeqj.de/sneak/secret/issues/137). `current-unlocker` went on

internal/cli/generate.go

@@ -103,7 +103,7 @@ func (cli *Instance) GenerateMnemonic(cmd *cobra.Command) error {
 	}
 
 	// Output mnemonic to stdout
-	cmd.Println(mnemonic)
+	_, _ = fmt.Fprintln(cmd.OutOrStdout(), mnemonic)
 
 	// Output helpful information to stderr
 	fmt.Fprintln(os.Stderr, "")

internal/cli/secrets.go

@@ -443,7 +443,10 @@ func (cli *Instance) GetSecret(cmd *cobra.Command, secretName string) error {
 	defer value.Destroy()
 
 	// Write the value straight from locked memory, with no trailing newline
-	_, _ = cmd.OutOrStdout().Write(value.Bytes())
+	_, err = cmd.OutOrStdout().Write(value.Bytes())
+	if err != nil {
+		return fmt.Errorf("failed to write secret value: %w", err)
+	}
 
 	return nil
 }
@@ -478,7 +481,10 @@ func (cli *Instance) GetSecretWithVersion(
 	secret.Debug("Got secret value", "valueLength", value.Size())
 
 	// Write the value straight from locked memory, with no trailing newline
-	_, _ = cmd.OutOrStdout().Write(value.Bytes())
+	_, err = cmd.OutOrStdout().Write(value.Bytes())
+	if err != nil {
+		return fmt.Errorf("failed to write secret value: %w", err)
+	}
 
 	secret.Debug("Printed value to stdout")
 

internal/cli/stdout_stderr_test.go

@@ -2,6 +2,7 @@ package cli_test
 
 import (
 	"bytes"
+	"encoding/json"
 	"os/exec"
 	"path/filepath"
 	"strings"
@@ -9,6 +10,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/secret/internal/bip39"
 	"sneak.berlin/go/secret/internal/secret"
 )
 
@@ -90,3 +92,66 @@ func TestGetCommandOutputsToStdout(t *testing.T) {
 	// Nothing should be in stderr
 	assert.Empty(t, stderr.String(), "stderr should be empty")
 }
+
+// TestMnemonicAndListingsOutputToStdout tests that 'secret generate
+// mnemonic', 'secret vault list' and 'secret unlocker list' print their
+// output to stdout, so that it can be piped
+func TestMnemonicAndListingsOutputToStdout(t *testing.T) {
+	t.Parallel()
+
+	tempDir := t.TempDir()
+	secretPath := secretBinaryPath(t)
+
+	// run runs the secret binary and returns what it wrote to stdout and to
+	// stderr
+	run := func(args ...string) (string, string) {
+		//nolint:gosec // G204: test executes the freshly built secret binary
+		cmd := exec.CommandContext(t.Context(), secretPath, args...)
+		cmd.Env = []string{
+			secret.EnvStateDir + "=" + tempDir,
+			secret.EnvMnemonic + "=" + testMnemonic,
+			secret.EnvUnlockPassphrase + "=test-passphrase",
+			"PATH=/usr/bin:/bin",
+		}
+
+		var stdout, stderr bytes.Buffer
+
+		cmd.Stdout = &stdout
+		cmd.Stderr = &stderr
+
+		err := cmd.Run()
+		require.NoError(t, err, "%v should succeed: %s", args, stderr.String())
+
+		return stdout.String(), stderr.String()
+	}
+
+	stdout, stderr := run("generate", "mnemonic")
+	assert.True(t, bip39.IsMnemonicValid(strings.TrimSpace(stdout)),
+		"stdout should hold the mnemonic, not %q", stdout)
+	assert.Contains(t, stderr, "Save this mnemonic phrase securely",
+		"the warning should be on stderr")
+
+	run("init")
+
+	stdout, _ = run("vault", "list", "--json")
+
+	var vaults map[string]any
+
+	require.NoError(t, json.Unmarshal([]byte(stdout), &vaults),
+		"stdout should hold the vaults as JSON, not %q", stdout)
+	assert.Equal(t, "default", vaults["currentVault"])
+
+	stdout, _ = run("unlocker", "list", "--json")
+
+	var unlockers map[string]any
+
+	require.NoError(t, json.Unmarshal([]byte(stdout), &unlockers),
+		"stdout should hold the unlockers as JSON, not %q", stdout)
+	assert.Len(t, unlockers["unlockers"], 1)
+
+	stdout, _ = run("vault", "list")
+	assert.Contains(t, stdout, "default (current)")
+
+	stdout, _ = run("unlocker", "list")
+	assert.Contains(t, stdout, "Total: 1 unlocker(s)")
+}

internal/cli/unlockers.go

@@ -326,22 +326,25 @@ func (cli *Instance) printUnlockersJSON(
 		return fmt.Errorf("failed to marshal JSON: %w", err)
 	}
 
-	cli.cmd.Println(string(jsonBytes))
+	_, _ = fmt.Fprintln(cli.cmd.OutOrStdout(), string(jsonBytes))
 
 	return nil
 }
 
 // printUnlockersTable prints unlockers in a formatted table
 func (cli *Instance) printUnlockersTable(unlockers []UnlockerInfo) error {
+	out := cli.cmd.OutOrStdout()
+
 	if len(unlockers) == 0 {
-		cli.cmd.Println("No unlockers found in current vault.")
-		cli.cmd.Println("Run 'secret unlocker add passphrase' to create one.")
+		_, _ = fmt.Fprintln(out, "No unlockers found in current vault.")
+		_, _ = fmt.Fprintln(out, "Run 'secret unlocker add passphrase' to create one.")
 
 		return nil
 	}
 
-	cli.cmd.Printf("  %-40s %-12s %-20s %s\n", "UNLOCKER ID", "TYPE", "CREATED", "FLAGS")
-	cli.cmd.Printf("  %-40s %-12s %-20s %s\n",
+	_, _ = fmt.Fprintf(out, "  %-40s %-12s %-20s %s\n",
+		"UNLOCKER ID", "TYPE", "CREATED", "FLAGS")
+	_, _ = fmt.Fprintf(out, "  %-40s %-12s %-20s %s\n",
 		strings.Repeat("-", unlockerIDWidth), strings.Repeat("-", unlockerTypeWidth),
 		strings.Repeat("-", unlockerDateWidth), strings.Repeat("-", unlockerFlagsWidth))
 
@@ -356,7 +359,7 @@ func (cli *Instance) printUnlockersTable(unlockers []UnlockerInfo) error {
 			prefix = "* "
 		}
 
-		cli.cmd.Printf("%s%-40s %-12s %-20s %s\n",
+		_, _ = fmt.Fprintf(out, "%s%-40s %-12s %-20s %s\n",
 			prefix,
 			unlocker.ID,
 			unlocker.Type,
@@ -364,7 +367,7 @@ func (cli *Instance) printUnlockersTable(unlockers []UnlockerInfo) error {
 			flags)
 	}
 
-	cli.cmd.Printf("\nTotal: %d unlocker(s)\n", len(unlockers))
+	_, _ = fmt.Fprintf(out, "\nTotal: %d unlocker(s)\n", len(unlockers))
 
 	return nil
 }

internal/cli/vault.go

@@ -186,6 +186,8 @@ func (cli *Instance) ListVaults(cmd *cobra.Command, jsonOutput bool) error {
 		return err
 	}
 
+	out := cmd.OutOrStdout()
+
 	if jsonOutput { //nolint:nestif // Separate JSON and text output formatting logic
 		// Get current vault name for context
 		currentVault := ""
@@ -205,13 +207,13 @@ func (cli *Instance) ListVaults(cmd *cobra.Command, jsonOutput bool) error {
 			return err
 		}
 
-		cmd.Println(string(jsonBytes))
+		_, _ = fmt.Fprintln(out, string(jsonBytes))
 	} else {
 		// Text output
-		cmd.Println("Available vaults:")
+		_, _ = fmt.Fprintln(out, "Available vaults:")
 
 		if len(vaults) == 0 {
-			cmd.Println("  (none)")
+			_, _ = fmt.Fprintln(out, "  (none)")
 		} else {
 			// Try to get current vault for marking
 			currentVault := ""
@@ -223,9 +225,9 @@ func (cli *Instance) ListVaults(cmd *cobra.Command, jsonOutput bool) error {
 
 			for _, vaultName := range vaults {
 				if vaultName == currentVault {
-					cmd.Printf("  %s (current)\n", vaultName)
+					_, _ = fmt.Fprintf(out, "  %s (current)\n", vaultName)
 				} else {
-					cmd.Printf("  %s\n", vaultName)
+					_, _ = fmt.Fprintf(out, "  %s\n", vaultName)
 				}
 			}
 		}

internal/cli/version.go

@@ -167,7 +167,7 @@ func (cli *Instance) ListVersions(cmd *cobra.Command, secretName string) error {
 	}
 
 	if len(versions) == 0 {
-		cmd.Println("No versions found")
+		_, _ = fmt.Fprintln(cmd.OutOrStdout(), "No versions found")
 
 		return nil
 	}

internal/cli/version_test.go

@@ -8,6 +8,7 @@
 // - TestPromoteNonExistentVersion: Tests error handling for invalid promotion
 // - TestGetSecretWithVersion: Tests `secret get --version` flag functionality
 // - TestGetSecretWritesBinaryValue: Tests `secret get` output of binary values
+// - TestGetSecretReturnsWriteError: Tests `secret get` when stdout fails
 // - TestVersionCommandStructure: Tests command structure and help text
 // - TestListVersionsEmptyOutput: Tests edge case with no versions
 //
@@ -20,6 +21,7 @@ package cli
 
 import (
 	"bytes"
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -360,6 +362,45 @@ func TestGetSecretWritesBinaryValue(t *testing.T) {
 	assert.Equal(t, value, buf.Bytes())
 }
 
+// TestGetSecretReturnsWriteError checks that `secret get`, with and without
+// a version, returns the error of a failed write of the value.
+func TestGetSecretReturnsWriteError(t *testing.T) {
+	t.Parallel()
+
+	fs := afero.NewMemMapFs()
+	cli := NewCLIInstanceWithStateDir(fs, testStateDir)
+	cli.Mnemonic = testMnemonicBuffer(t)
+
+	setupTestVault(t, fs)
+
+	vlt, err := vault.GetCurrentVault(fs, testStateDir)
+	require.NoError(t, err)
+
+	addTestSecret(t, vlt, []byte("value"), false)
+
+	vaultDir, err := vlt.GetDirectory()
+	require.NoError(t, err)
+
+	versions, err := secret.ListVersions(fs,
+		filepath.Join(vaultDir, "secrets.d", "test%secret"))
+	require.NoError(t, err)
+	require.Len(t, versions, 1)
+
+	// Stdout is a file closed before the value is written to it
+	out, err := os.Create(filepath.Join(t.TempDir(), "stdout"))
+	require.NoError(t, err)
+	require.NoError(t, out.Close())
+
+	cmd := newRootCmd()
+	cmd.SetOut(out)
+
+	err = cli.GetSecret(cmd, "test/secret")
+	require.ErrorIs(t, err, os.ErrClosed)
+
+	err = cli.GetSecretWithVersion(cmd, "test/secret", versions[0])
+	require.ErrorIs(t, err, os.ErrClosed)
+}
+
 //nolint:paralleltest // reads process environment to determine the state dir
 func TestVersionCommandStructure(t *testing.T) {
 	// Test that version commands are properly structured