example_test.go

Documentation: os/exec

		 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  	"log"
		14  	"os"
		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 ExampleCommand_environment() {
		41  	cmd := exec.Command("prog")
		42  	cmd.Env = append(os.Environ(),
		43  		"FOO=duplicate_value", // ignored
		44  		"FOO=actual_value",		// this value is used
		45  	)
		46  	if err := cmd.Run(); err != nil {
		47  		log.Fatal(err)
		48  	}
		49  }
		50  
		51  func ExampleCmd_Output() {
		52  	out, err := exec.Command("date").Output()
		53  	if err != nil {
		54  		log.Fatal(err)
		55  	}
		56  	fmt.Printf("The date is %s\n", out)
		57  }
		58  
		59  func ExampleCmd_Run() {
		60  	cmd := exec.Command("sleep", "1")
		61  	log.Printf("Running command and waiting for it to finish...")
		62  	err := cmd.Run()
		63  	log.Printf("Command finished with error: %v", err)
		64  }
		65  
		66  func ExampleCmd_Start() {
		67  	cmd := exec.Command("sleep", "5")
		68  	err := cmd.Start()
		69  	if err != nil {
		70  		log.Fatal(err)
		71  	}
		72  	log.Printf("Waiting for command to finish...")
		73  	err = cmd.Wait()
		74  	log.Printf("Command finished with error: %v", err)
		75  }
		76  
		77  func ExampleCmd_StdoutPipe() {
		78  	cmd := exec.Command("echo", "-n", `{"Name": "Bob", "Age": 32}`)
		79  	stdout, err := cmd.StdoutPipe()
		80  	if err != nil {
		81  		log.Fatal(err)
		82  	}
		83  	if err := cmd.Start(); err != nil {
		84  		log.Fatal(err)
		85  	}
		86  	var person struct {
		87  		Name string
		88  		Age	int
		89  	}
		90  	if err := json.NewDecoder(stdout).Decode(&person); err != nil {
		91  		log.Fatal(err)
		92  	}
		93  	if err := cmd.Wait(); err != nil {
		94  		log.Fatal(err)
		95  	}
		96  	fmt.Printf("%s is %d years old\n", person.Name, person.Age)
		97  }
		98  
		99  func ExampleCmd_StdinPipe() {
	 100  	cmd := exec.Command("cat")
	 101  	stdin, err := cmd.StdinPipe()
	 102  	if err != nil {
	 103  		log.Fatal(err)
	 104  	}
	 105  
	 106  	go func() {
	 107  		defer stdin.Close()
	 108  		io.WriteString(stdin, "values written to stdin are passed to cmd's standard input")
	 109  	}()
	 110  
	 111  	out, err := cmd.CombinedOutput()
	 112  	if err != nil {
	 113  		log.Fatal(err)
	 114  	}
	 115  
	 116  	fmt.Printf("%s\n", out)
	 117  }
	 118  
	 119  func ExampleCmd_StderrPipe() {
	 120  	cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
	 121  	stderr, err := cmd.StderrPipe()
	 122  	if err != nil {
	 123  		log.Fatal(err)
	 124  	}
	 125  
	 126  	if err := cmd.Start(); err != nil {
	 127  		log.Fatal(err)
	 128  	}
	 129  
	 130  	slurp, _ := io.ReadAll(stderr)
	 131  	fmt.Printf("%s\n", slurp)
	 132  
	 133  	if err := cmd.Wait(); err != nil {
	 134  		log.Fatal(err)
	 135  	}
	 136  }
	 137  
	 138  func ExampleCmd_CombinedOutput() {
	 139  	cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
	 140  	stdoutStderr, err := cmd.CombinedOutput()
	 141  	if err != nil {
	 142  		log.Fatal(err)
	 143  	}
	 144  	fmt.Printf("%s\n", stdoutStderr)
	 145  }
	 146  
	 147  func ExampleCommandContext() {
	 148  	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
	 149  	defer cancel()
	 150  
	 151  	if err := exec.CommandContext(ctx, "sleep", "5").Run(); err != nil {
	 152  		// This will fail after 100 milliseconds. The 5 second sleep
	 153  		// will be interrupted.
	 154  	}
	 155  }
	 156
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