github.com/slayercat/go@v0.0.0-20170428012452-c51559813f61/src/os/exec/example_test.go (about)

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