Go exec

Package exec runs external commands. It wraps os.StartProcess to make it easier to remap stdin and stdout, connect I/O with pipes, and do other adjustments.

func LookPath

func LookPath(file string) (string, error)

LookPath searches for an executable binary named file in the directories named by the PATH environment variable. If file contains a slash, it is tried directly and the PATH is not consulted. The result may be an absolute path or a path relative to the current directory.

package main

import (
    "fmt"
    "log"
    "os/exec"
)

func main() {
    path, err := exec.LookPath("fortune")
    if err != nil {
        log.Fatal("installing fortune is in your future")
    }
    fmt.Printf("fortune is available at %s\n", path)
}

func (*Cmd) Output

func (c *Cmd) Output() ([]byte, error)

Output runs the command and returns its standard output.

package main

import (
    "fmt"
    "log"
    "os/exec"
)

func main() {
    out, err := exec.Command("date").Output()
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("The date is %s\n", out)
}

func (*Cmd) Start

func (c *Cmd) Start() error

Start starts the specified command but does not wait for it to complete.

The Wait method will return the exit code and release associated resources once the command exits.

package main

import (
    "log"
    "os/exec"
)

func main() {
    cmd := exec.Command("sleep", "5")
    err := cmd.Start()
    if err != nil {
        log.Fatal(err)
    }
    log.Printf("Waiting for command to finish...")
    err = cmd.Wait()
    log.Printf("Command finished with error: %v", err)
}

func (*Cmd) StdoutPipe

func (c *Cmd) StdoutPipe() (io.ReadCloser, error)

StdoutPipe returns a pipe that will be connected to the command's standard output when the command starts.

Wait will close the pipe after seeing the command exit, so most callers need not close the pipe themselves; however, an implication is that it is incorrect to call Wait before all reads from the pipe have completed. For the same reason, it is incorrect to call Run when using StdoutPipe. See the example for idiomatic usage.

package main

import (
    "encoding/json"
    "fmt"
    "log"
    "os/exec"
)

func main() {
    cmd := exec.Command("echo", "-n", `{"Name": "Bob", "Age": 32}`)
    stdout, err := cmd.StdoutPipe()
    if err != nil {
        log.Fatal(err)
    }
    if err := cmd.Start(); err != nil {
        log.Fatal(err)
    }
    var person struct {
        Name string
        Age  int
    }
    if err := json.NewDecoder(stdout).Decode(&person); err != nil {
        log.Fatal(err)
    }
    if err := cmd.Wait(); err != nil {
        log.Fatal(err)
    }
    fmt.Printf("%s is %d years old\n", person.Name, person.Age)
}

func Command

func Command(name string, arg ...string) *Cmd

Command returns the Cmd struct to execute the named program with the given arguments.

It sets only the Path and Args in the returned structure.

If name contains no path separators, Command uses LookPath to resolve the path to a complete name if possible. Otherwise it uses name directly.

The returned Cmd's Args field is constructed from the command name followed by the elements of arg, so arg should not include the command name itself. For example, Command("echo", "hello")

package main

import (
    "bytes"
    "fmt"
    "log"
    "os/exec"
    "strings"
)

func main() {
    cmd := exec.Command("tr", "a-z", "A-Z")
    cmd.Stdin = strings.NewReader("some input")
    var out bytes.Buffer
    cmd.Stdout = &out
    err := cmd.Run()
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("in all caps: %q\n", out.String())
}

GO EXEC