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      1 // Copyright 2012 The Go Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 package exec_test
      6 
      7 import (
      8 	"bytes"
      9 	"context"
     10 	"encoding/json"
     11 	"fmt"
     12 	"io"
     13 	"io/ioutil"
     14 	"log"
     15 	"os/exec"
     16 	"strings"
     17 	"time"
     18 )
     19 
     20 func ExampleLookPath() {
     21 	path, err := exec.LookPath("fortune")
     22 	if err != nil {
     23 		log.Fatal("installing fortune is in your future")
     24 	}
     25 	fmt.Printf("fortune is available at %s\n", path)
     26 }
     27 
     28 func ExampleCommand() {
     29 	cmd := exec.Command("tr", "a-z", "A-Z")
     30 	cmd.Stdin = strings.NewReader("some input")
     31 	var out bytes.Buffer
     32 	cmd.Stdout = &out
     33 	err := cmd.Run()
     34 	if err != nil {
     35 		log.Fatal(err)
     36 	}
     37 	fmt.Printf("in all caps: %q\n", out.String())
     38 }
     39 
     40 func ExampleCmd_Output() {
     41 	out, err := exec.Command("date").Output()
     42 	if err != nil {
     43 		log.Fatal(err)
     44 	}
     45 	fmt.Printf("The date is %s\n", out)
     46 }
     47 
     48 func ExampleCmd_Start() {
     49 	cmd := exec.Command("sleep", "5")
     50 	err := cmd.Start()
     51 	if err != nil {
     52 		log.Fatal(err)
     53 	}
     54 	log.Printf("Waiting for command to finish...")
     55 	err = cmd.Wait()
     56 	log.Printf("Command finished with error: %v", err)
     57 }
     58 
     59 func ExampleCmd_StdoutPipe() {
     60 	cmd := exec.Command("echo", "-n", `{"Name": "Bob", "Age": 32}`)
     61 	stdout, err := cmd.StdoutPipe()
     62 	if err != nil {
     63 		log.Fatal(err)
     64 	}
     65 	if err := cmd.Start(); err != nil {
     66 		log.Fatal(err)
     67 	}
     68 	var person struct {
     69 		Name string
     70 		Age  int
     71 	}
     72 	if err := json.NewDecoder(stdout).Decode(&person); err != nil {
     73 		log.Fatal(err)
     74 	}
     75 	if err := cmd.Wait(); err != nil {
     76 		log.Fatal(err)
     77 	}
     78 	fmt.Printf("%s is %d years old\n", person.Name, person.Age)
     79 }
     80 
     81 func ExampleCmd_StdinPipe() {
     82 	cmd := exec.Command("cat")
     83 	stdin, err := cmd.StdinPipe()
     84 	if err != nil {
     85 		log.Fatal(err)
     86 	}
     87 
     88 	go func() {
     89 		defer stdin.Close()
     90 		io.WriteString(stdin, "values written to stdin are passed to cmd's standard input")
     91 	}()
     92 
     93 	out, err := cmd.CombinedOutput()
     94 	if err != nil {
     95 		log.Fatal(err)
     96 	}
     97 
     98 	fmt.Printf("%s\n", out)
     99 }
    100 
    101 func ExampleCmd_StderrPipe() {
    102 	cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
    103 	stderr, err := cmd.StderrPipe()
    104 	if err != nil {
    105 		log.Fatal(err)
    106 	}
    107 
    108 	if err := cmd.Start(); err != nil {
    109 		log.Fatal(err)
    110 	}
    111 
    112 	slurp, _ := ioutil.ReadAll(stderr)
    113 	fmt.Printf("%s\n", slurp)
    114 
    115 	if err := cmd.Wait(); err != nil {
    116 		log.Fatal(err)
    117 	}
    118 }
    119 
    120 func ExampleCmd_CombinedOutput() {
    121 	cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
    122 	stdoutStderr, err := cmd.CombinedOutput()
    123 	if err != nil {
    124 		log.Fatal(err)
    125 	}
    126 	fmt.Printf("%s\n", stdoutStderr)
    127 }
    128 
    129 func ExampleCommandContext() {
    130 	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
    131 	defer cancel()
    132 
    133 	if err := exec.CommandContext(ctx, "sleep", "5").Run(); err != nil {
    134 		// This will fail after 100 milliseconds. The 5 second sleep
    135 		// will be interrupted.
    136 	}
    137 }
    138