feat: add log rotation via newsyslog

README.ja.md

@@ -239,6 +239,17 @@ tail -f ~/Library/Logs/ldcron/a1b2c3d4.log
 tail -n 100 ~/Library/Logs/ldcron/a1b2c3d4.log
 ```
 
+### ログローテーション
+
+ログファイルはデフォルトでは無限に増え続けます。ldcronはnewsyslog(8)の設定を生成するコマンドを提供しており、すべてのldcronログファイルを自動的にローテーションできます。
+
+```bash
+# newsyslog設定を生成・インストール（初回のみ、sudo必要）
+ldcron log setup-rotation | sudo tee /etc/newsyslog.d/com.ldcron.conf
+```
+
+生成される設定は、各ログファイルが1MBを超えた時点でローテーションし、gzip圧縮したアーカイブを3世代保持します。プロセスへのシグナル送信は不要です（launchdはジョブ実行ごとにログファイルを開き直すため）。newsyslogはシステムのlaunchdジョブにより毎時自動実行されるため、追加のスケジュール設定は不要です。
+
 ---
 
 ## ファイル配置

README.md

@@ -239,6 +239,22 @@ tail -f ~/Library/Logs/ldcron/a1b2c3d4.log
 tail -n 100 ~/Library/Logs/ldcron/a1b2c3d4.log
 ```
 
+### Log rotation
+
+Log files grow indefinitely by default. ldcron provides a command to generate
+a newsyslog(8) configuration that automatically rotates all ldcron log files.
+
+```bash
+# Generate and install the newsyslog config (one-time setup, requires sudo)
+ldcron log setup-rotation | sudo tee /etc/newsyslog.d/com.ldcron.conf
+```
+
+The generated configuration rotates each log file when it exceeds 1 MB,
+keeps 3 compressed (gzip) archives, and requires no process signaling
+(launchd reopens log files on each job execution). newsyslog runs
+automatically every hour via a system launchd job, so no additional
+scheduling is needed.
+
 ---
 
 ## File locations

cmd/log.go

@@ -0,0 +1,56 @@
+package cmd
+
+import (
+	"fmt"
+	"path/filepath"
+
+	"github.com/spf13/cobra"
+)
+
+var logCmd = &cobra.Command{
+	Use:          "log",
+	Short:        "Manage job log files",
+	SilenceUsage: true,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		return cmd.Help()
+	},
+}
+
+var logSetupRotationCmd = &cobra.Command{
+	Use:   "setup-rotation",
+	Short: "Print newsyslog configuration for log rotation",
+	Long: `Print a newsyslog(8) configuration snippet that rotates ldcron log files.
+
+The generated configuration uses a glob pattern to cover all ldcron log files
+under ~/Library/Logs/ldcron/. newsyslog is a macOS system service that runs
+every hour and rotates log files according to /etc/newsyslog.d/*.conf.
+
+To install:
+  ldcron log setup-rotation | sudo tee /etc/newsyslog.d/com.ldcron.conf
+
+The configuration rotates logs when they exceed 1 MB, keeps 3 compressed
+archives, and requires no process signaling.`,
+	SilenceUsage: true,
+	RunE:         runLogSetupRotation,
+}
+
+func init() {
+	logCmd.AddCommand(logSetupRotationCmd)
+}
+
+func runLogSetupRotation(cmd *cobra.Command, _ []string) error {
+	dir, err := logDirPath()
+	if err != nil {
+		return err
+	}
+	logPattern := filepath.Join(dir, "*.log")
+
+	w := cmd.OutOrStdout()
+	_, _ = fmt.Fprintf(w, "# ldcron log rotation — managed by ldcron\n")
+	_, _ = fmt.Fprintf(w, "# See newsyslog.conf(5) for format details.\n")
+	_, _ = fmt.Fprintf(w, "# logfilename\t\t\t\t\t\tmode\tcount\tsize\twhen\tflags\n")
+	// Flags: G=glob pattern, N=no signal to any process,
+	// B=don't insert a rotation-marker line into the new log file
+	_, _ = fmt.Fprintf(w, "%s\t644\t3\t1024\t*\tGNB\n", logPattern)
+	return nil
+}

cmd/log_test.go

@@ -0,0 +1,41 @@
+package cmd
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestLogSetupRotation(t *testing.T) {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantPattern := filepath.Join(home, "Library", "Logs", "ldcron", "*.log")
+
+	var buf bytes.Buffer
+	cmd := logSetupRotationCmd
+	cmd.SetOut(&buf)
+	t.Cleanup(func() { cmd.SetOut(nil) })
+
+	if err := cmd.RunE(cmd, nil); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	output := buf.String()
+
+	if !strings.Contains(output, wantPattern) {
+		t.Errorf("output should contain log pattern %q, got:\n%s", wantPattern, output)
+	}
+	if !strings.Contains(output, "GNB") {
+		t.Errorf("output should contain flags GNB, got:\n%s", output)
+	}
+	if !strings.Contains(output, "1024") {
+		t.Errorf("output should contain size 1024, got:\n%s", output)
+	}
+	if !strings.Contains(output, "644") {
+		t.Errorf("output should contain mode 644, got:\n%s", output)
+	}
+}

cmd/paths.go

@@ -14,12 +14,19 @@ func launchAgentsDir() (string, error) {
 	return filepath.Join(home, "Library", "LaunchAgents"), nil
 }
 
-func logDir() (string, error) {
+func logDirPath() (string, error) {
 	home, err := os.UserHomeDir()
 	if err != nil {
 		return "", fmt.Errorf("failed to get home directory: %w", err)
 	}
-	dir := filepath.Join(home, "Library", "Logs", "ldcron")
+	return filepath.Join(home, "Library", "Logs", "ldcron"), nil
+}
+
+func logDir() (string, error) {
+	dir, err := logDirPath()
+	if err != nil {
+		return "", err
+	}
 	if err := os.MkdirAll(dir, 0o755); err != nil {
 		return "", fmt.Errorf("failed to create log directory: %w", err)
 	}

cmd/root.go

@@ -34,6 +34,7 @@ func init() {
 	rootCmd.AddCommand(listCmd)
 	rootCmd.AddCommand(removeCmd)
 	rootCmd.AddCommand(runCmd)
+	rootCmd.AddCommand(logCmd)
 
 	// Save the default subcommand help, then set a custom help for the root command.
 	defaultHelp := rootCmd.HelpFunc()
@@ -76,6 +77,7 @@ Commands:
   list                                     List all registered jobs
   remove  <id>                             Delete a job by ID
   run     <id>                             Run a job immediately
+  log     setup-rotation                   Print newsyslog config for log rotation
 
 Cron expression format (minute hour day month weekday):
 
@@ -84,6 +86,10 @@ Cron expression format (minute hour day month weekday):
   "0 9 * * 1-5"    Weekdays (Mon–Fri) at 9:00
   "30 8 1 * *"     1st of every month at 8:30
 
+Log rotation:
+
+  ldcron log setup-rotation | sudo tee /etc/newsyslog.d/com.ldcron.conf
+
 Flags:
 
   -h, --help      Show this help message