example_test.go

     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  	"context"
     9  	"encoding/json"
    10  	"fmt"
    11  	"io"
    12  	"log"
    13  	"os"
    14  	"os/exec"
    15  	"strings"
    16  	"time"
    17  )
    18  
    19  func ExampleLookPath() {
    20  	path, err := exec.LookPath("fortune")
    21  	if err != nil {
    22  		log.Fatal("installing fortune is in your future")
    23  	}
    24  	fmt.Printf("fortune is available at %s\n", path)
    25  }
    26  
    27  func ExampleCommand() {
    28  	cmd := exec.Command("tr", "a-z", "A-Z")
    29  	cmd.Stdin = strings.NewReader("some input")
    30  	var out strings.Builder
    31  	cmd.Stdout = &out
    32  	err := cmd.Run()
    33  	if err != nil {
    34  		log.Fatal(err)
    35  	}
    36  	fmt.Printf("in all caps: %q\n", out.String())
    37  }
    38  
    39  func ExampleCommand_environment() {
    40  	cmd := exec.Command("prog")
    41  	cmd.Env = append(os.Environ(),
    42  		"FOO=duplicate_value", // ignored
    43  		"FOO=actual_value",    // this value is used
    44  	)
    45  	if err := cmd.Run(); err != nil {
    46  		log.Fatal(err)
    47  	}
    48  }
    49  
    50  func ExampleCmd_Output() {
    51  	out, err := exec.Command("date").Output()
    52  	if err != nil {
    53  		log.Fatal(err)
    54  	}
    55  	fmt.Printf("The date is %s\n", out)
    56  }
    57  
    58  func ExampleCmd_Run() {
    59  	cmd := exec.Command("sleep", "1")
    60  	log.Printf("Running command and waiting for it to finish...")
    61  	err := cmd.Run()
    62  	log.Printf("Command finished with error: %v", err)
    63  }
    64  
    65  func ExampleCmd_Start() {
    66  	cmd := exec.Command("sleep", "5")
    67  	err := cmd.Start()
    68  	if err != nil {
    69  		log.Fatal(err)
    70  	}
    71  	log.Printf("Waiting for command to finish...")
    72  	err = cmd.Wait()
    73  	log.Printf("Command finished with error: %v", err)
    74  }
    75  
    76  func ExampleCmd_StdoutPipe() {
    77  	cmd := exec.Command("echo", "-n", `{"Name": "Bob", "Age": 32}`)
    78  	stdout, err := cmd.StdoutPipe()
    79  	if err != nil {
    80  		log.Fatal(err)
    81  	}
    82  	if err := cmd.Start(); err != nil {
    83  		log.Fatal(err)
    84  	}
    85  	var person struct {
    86  		Name string
    87  		Age  int
    88  	}
    89  	if err := json.NewDecoder(stdout).Decode(&person); err != nil {
    90  		log.Fatal(err)
    91  	}
    92  	if err := cmd.Wait(); err != nil {
    93  		log.Fatal(err)
    94  	}
    95  	fmt.Printf("%s is %d years old\n", person.Name, person.Age)
    96  }
    97  
    98  func ExampleCmd_StdinPipe() {
    99  	cmd := exec.Command("cat")
   100  	stdin, err := cmd.StdinPipe()
   101  	if err != nil {
   102  		log.Fatal(err)
   103  	}
   104  
   105  	go func() {
   106  		defer stdin.Close()
   107  		io.WriteString(stdin, "values written to stdin are passed to cmd's standard input")
   108  	}()
   109  
   110  	out, err := cmd.CombinedOutput()
   111  	if err != nil {
   112  		log.Fatal(err)
   113  	}
   114  
   115  	fmt.Printf("%s\n", out)
   116  }
   117  
   118  func ExampleCmd_StderrPipe() {
   119  	cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
   120  	stderr, err := cmd.StderrPipe()
   121  	if err != nil {
   122  		log.Fatal(err)
   123  	}
   124  
   125  	if err := cmd.Start(); err != nil {
   126  		log.Fatal(err)
   127  	}
   128  
   129  	slurp, _ := io.ReadAll(stderr)
   130  	fmt.Printf("%s\n", slurp)
   131  
   132  	if err := cmd.Wait(); err != nil {
   133  		log.Fatal(err)
   134  	}
   135  }
   136  
   137  func ExampleCmd_CombinedOutput() {
   138  	cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
   139  	stdoutStderr, err := cmd.CombinedOutput()
   140  	if err != nil {
   141  		log.Fatal(err)
   142  	}
   143  	fmt.Printf("%s\n", stdoutStderr)
   144  }
   145  
   146  func ExampleCmd_Environ() {
   147  	cmd := exec.Command("pwd")
   148  
   149  	// Set Dir before calling cmd.Environ so that it will include an
   150  	// updated PWD variable (on platforms where that is used).
   151  	cmd.Dir = ".."
   152  	cmd.Env = append(cmd.Environ(), "POSIXLY_CORRECT=1")
   153  
   154  	out, err := cmd.Output()
   155  	if err != nil {
   156  		log.Fatal(err)
   157  	}
   158  	fmt.Printf("%s\n", out)
   159  }
   160  
   161  func ExampleCommandContext() {
   162  	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
   163  	defer cancel()
   164  
   165  	if err := exec.CommandContext(ctx, "sleep", "5").Run(); err != nil {
   166  		// This will fail after 100 milliseconds. The 5 second sleep
   167  		// will be interrupted.
   168  	}
   169  }
   170
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