Get exit code - Go

I'm using the package: os/exec http://golang.org/pkg/os/exec/ to execute a command in the operating system but I don't seem to find the way to get the exit code. I can read the output though

ie.

package main

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

func main() {
    cmd := exec.Command("somecommand", "parameter")
    var out bytes.Buffer
    cmd.Stdout = &out
    if err := cmd.Run() ; err != nil {
        //log.Fatal( cmd.ProcessState.Success() )
        log.Fatal( err )
    }
    fmt.Printf("%q\n", out.String() )
}

Solution 1:

It's easy to determine if the exit code was 0 or something else. In the first case, cmd.Wait() will return nil (unless there is another error while setting up the pipes).

Unfortunately, there is no platform independent way to get the exit code in the error case. That's also the reason why it isn't part of the API. The following snippet will work with Linux, but I haven't tested it on other platforms:

package main

import "os/exec"
import "log"
import "syscall"

func main() {
    cmd := exec.Command("git", "blub")

    if err := cmd.Start(); err != nil {
        log.Fatalf("cmd.Start: %v", err)
    }

    if err := cmd.Wait(); err != nil {
        if exiterr, ok := err.(*exec.ExitError); ok {
            // The program has exited with an exit code != 0

            // This works on both Unix and Windows. Although package
            // syscall is generally platform dependent, WaitStatus is
            // defined for both Unix and Windows and in both cases has
            // an ExitStatus() method with the same signature.
            if status, ok := exiterr.Sys().(syscall.WaitStatus); ok {
                log.Printf("Exit Status: %d", status.ExitStatus())
            }
        } else {
            log.Fatalf("cmd.Wait: %v", err)
        }
    }
}

Just follow the api docs to find out more :)

Solution 2:

Since golang version 1.12, the exit code is available natively and in a cross-platform manner. See ExitError and ExitCode().

ExitCode returns the exit code of the exited process, or -1 if the process hasn't exited or was terminated by a signal.

if err := cmd.Run() ; err != nil {
    if exitError, ok := err.(*exec.ExitError); ok {
        return exitError.ExitCode()
    }
}

Solution 3:

Here's my enhanced version based on @tux21b 's answer

utils/cmd.go

package utils

import (
    "bytes"
    "log"
    "os/exec"
    "syscall"
)

const defaultFailedCode = 1

func RunCommand(name string, args ...string) (stdout string, stderr string, exitCode int) {
    log.Println("run command:", name, args)
    var outbuf, errbuf bytes.Buffer
    cmd := exec.Command(name, args...)
    cmd.Stdout = &outbuf
    cmd.Stderr = &errbuf

    err := cmd.Run()
    stdout = outbuf.String()
    stderr = errbuf.String()

    if err != nil {
        // try to get the exit code
        if exitError, ok := err.(*exec.ExitError); ok {
            ws := exitError.Sys().(syscall.WaitStatus)
            exitCode = ws.ExitStatus()
        } else {
            // This will happen (in OSX) if `name` is not available in $PATH,
            // in this situation, exit code could not be get, and stderr will be
            // empty string very likely, so we use the default fail code, and format err
            // to string and set to stderr
            log.Printf("Could not get exit code for failed program: %v, %v", name, args)
            exitCode = defaultFailedCode
            if stderr == "" {
                stderr = err.Error()
            }
        }
    } else {
        // success, exitCode should be 0 if go is ok
        ws := cmd.ProcessState.Sys().(syscall.WaitStatus)
        exitCode = ws.ExitStatus()
    }
    log.Printf("command result, stdout: %v, stderr: %v, exitCode: %v", stdout, stderr, exitCode)
    return
}

I have tested it on OSX, if it's not working as expected on other platforms, please tell me so we can make it better.

Solution 4:

September 2019, Go 1.13 introduced errors.As which supports error "unwrapping" - handy for finding precise errors in a nested call-chain.

So to extract and inspect the two most common errors when running an external command:

• os.PathError
• exec.ExitError

err := cmd.Run()

var (
    ee *exec.ExitError
    pe *os.PathError
)

if errors.As(err, &ee) {
    log.Println("exit code error:", ee.ExitCode()) // ran, but non-zero exit code

} else if errors.As(err, &pe) {
    log.Printf("os.PathError: %v", pe) // "no such file ...", "permission denied" etc.

} else if err != nil {
    log.Printf("general error: %v", err) // something really bad happened!

} else {
    log.Println("success!") // ran without error (exit code zero)
}