error handling in golang

errors.go

package main

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

// run quietly, unless there is an error
func main() {
	wd, err := os.Getwd()
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	result, err := gitVersion(wd)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	fmt.Println(result)

	result, err = gitLog(wd)
	// example of switch type assertion to convert interface value to concrete struct implementation
	// can be used to trigger certain behaviors off error subtypes
	if ee, ok := err.(*ErrExecution); ok {
		fmt.Fprintln(os.Stderr, "found an ErrExecution!", ee.Stderr)
		os.Exit(1)
	}
	if err != nil {
		fmt.Println(err)
	}
	fmt.Println(result)
}

func gitVersion(cwd string) (string, error) {
	return execute(cwd, "git", []string{"version"})
}

func gitLog(cwd string, args ...string) (string, error) {
	return execute(cwd, "git", append([]string{"log"}, args...))
}

type ErrExecution struct {
	error
	Cmd      *exec.Cmd
	ExitCode int
	Stderr   string
}

func (e ErrExecution) Error() string {
	joinedArgs := strings.Join(e.Cmd.Args, " ")
	return fmt.Sprintf(`
Error:      %v
Executable: %s
Command:    "%s"
Stderr:     %s`, e.error, e.Cmd.Path, joinedArgs, e.Stderr)
}

func execute(cwd string, command string, args []string) (string, error) {
	cmd := exec.Command(command, args...)
	stdout := bytes.Buffer{}
	stderr := bytes.Buffer{}
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr
	cmd.Dir = cwd
	err := cmd.Run()
	if err != nil {
		return "", &ErrExecution{error: err, Cmd: cmd, ExitCode: cmd.ProcessState.ExitCode(), Stderr: stderr.String()}
	}
	return stdout.String(), nil
}