cmd/dump: dump metadata into STDOUT (#551)

* dump metadata into STDOUT

* update docs

cmd/dump.go

@@ -17,6 +17,7 @@ package main
 
 import (
 	"fmt"
+	"io"
 	"os"
 
 	"github.com/juicedata/juicefs/pkg/meta"
@@ -25,16 +26,21 @@ import (
 
 func dump(ctx *cli.Context) error {
 	setLoggerLevel(ctx)
-	if ctx.Args().Len() < 2 {
-		return fmt.Errorf("META-ADDR and FILE are needed")
+	if ctx.Args().Len() < 1 {
+		return fmt.Errorf("META-ADDR is needed")
 	}
-	m := meta.NewClient(ctx.Args().Get(0), &meta.Config{Retries: 10, Strict: true, Subdir: ctx.String("subdir")})
-	fname := ctx.Args().Get(1)
-	fp, err := os.OpenFile(fname, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
-	if err != nil {
-		return err
+	var fp io.WriteCloser
+	if ctx.Args().Len() == 1 {
+		fp = os.Stdout
+	} else {
+		var err error
+		fp, err = os.OpenFile(ctx.Args().Get(1), os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
+		if err != nil {
+			return err
+		}
+		defer fp.Close()
 	}
-	defer fp.Close()
+	m := meta.NewClient(ctx.Args().Get(0), &meta.Config{Retries: 10, Strict: true, Subdir: ctx.String("subdir")})
 	return m.DumpMeta(fp)
 }
 
@@ -42,7 +48,7 @@ func dumpFlags() *cli.Command {
 	return &cli.Command{
 		Name:      "dump",
 		Usage:     "dump metadata into a JSON file",
-		ArgsUsage: "META-ADDR FILE",
+		ArgsUsage: "META-ADDR [FILE]",
 		Action:    dump,
 		Flags: []cli.Flag{
 			&cli.StringFlag{

cmd/load.go

@@ -18,6 +18,7 @@ package main
 import (
 	"fmt"
 	"io/ioutil"
+	"os"
 
 	"github.com/juicedata/juicefs/pkg/meta"
 	"github.com/urfave/cli/v2"
@@ -25,15 +26,20 @@ import (
 
 func load(ctx *cli.Context) error {
 	setLoggerLevel(ctx)
-	if ctx.Args().Len() < 2 {
-		return fmt.Errorf("META-ADDR and FILE are needed")
+	if ctx.Args().Len() < 1 {
+		return fmt.Errorf("META-ADDR is needed")
+	}
+	var buf []byte
+	var err error
+	if ctx.Args().Len() == 1 {
+		buf, err = ioutil.ReadAll(os.Stdin)
+	} else {
+		buf, err = ioutil.ReadFile(ctx.Args().Get(1))
 	}
-	m := meta.NewClient(ctx.Args().Get(0), &meta.Config{Retries: 10, Strict: true})
-	fname := ctx.Args().Get(1)
-	buf, err := ioutil.ReadFile(fname)
 	if err != nil {
 		return err
 	}
+	m := meta.NewClient(ctx.Args().Get(0), &meta.Config{Retries: 10, Strict: true})
 	return m.LoadMeta(buf)
 }
 
@@ -41,7 +47,7 @@ func loadFlags() *cli.Command {
 	return &cli.Command{
 		Name:      "load",
 		Usage:     "load metadata from a previously dumped JSON file",
-		ArgsUsage: "META-ADDR FILE",
+		ArgsUsage: "META-ADDR [FILE]",
 		Action:    load,
 	}
 }

docs/en/command_reference.md

@@ -525,9 +525,11 @@ dump metadata into a JSON file
 #### Synopsis
 
 ```
-juicefs dump [command options] META-ADDR FILE
+juicefs dump [command options] META-ADDR [FILE]
 ```
 
+When the FILE is not provided, STDOUT will be used instead.
+
 #### Options
 
 `--subdir value`\
@@ -542,5 +544,7 @@ load metadata from a previously dumped JSON file
 #### Synopsis
 
 ```
-juicefs load [command options] META-ADDR FILE
+juicefs load [command options] META-ADDR [FILE]
 ```
+
+When the FILE is not provided, STDIN will be used instead.

docs/zh_cn/command_reference.md

@@ -525,9 +525,11 @@ juicefs warmup [command options] [PATH ...]
 #### 使用
 
 ```
-juicefs dump [command options] META-ADDR FILE
+juicefs dump [command options] META-ADDR [FILE]
 ```
 
+如果没有指定导出文件路径，会导出到标准输出。
+
 #### 选项
 
 `--subdir value`\
@@ -542,5 +544,7 @@ juicefs dump [command options] META-ADDR FILE
 #### 使用
 
 ```
-juicefs load [command options] META-ADDR FILE
+juicefs load [command options] META-ADDR [FILE]
 ```
+
+如果没有指定导入文件路径，会从标准输入导入。