在Golang中使用输入重定向对diff进行外壳处理

Question

I'm trying to shell out something similar to:

diff  <(echo -e "$string1" ) <(echo -e "$string2")

in Golang but all my attempts with exec.Command have failed.

Here is the most naive attempt I have tried (CombinedOutput is temporarily used to get the underlying issue):

func Diff(str1, str2 string) (string, error) {
    cmd := exec.Command("diff", sanitize(str1), sanitize(str2))
    bytes, err := cmd.CombinedOutput()
    result := string(bytes)
    if err != nil {
        switch err.(type) {
        case *exec.ExitError:
            return result, nil
        default:
            return "", nil
        }
    }
    return result, nil
}

Which gives me results such as: diff: \"foo bar baz\": No such file or directory diff: \"foo fighters baz\": No such file or directory

A more involved version still does not work:

func Diff(str1, str2 string) (string, error) {
    cmd := exec.Command("diff")
    stdin, err := cmd.StdinPipe()
    if err != nil {
        return "", err
    }
    stdout, err := cmd.StdoutPipe()
    if err != nil {
        return "", err
    }
    err = cmd.Start()
    if err != nil {
        return "", err
    }
    io.WriteString(stdin, echoString(str1))
    io.WriteString(stdin, echoString(str2))
    bytes, err := ioutil.ReadAll(stdout)
    cmd.Wait()
    result := string(bytes)
    if err != nil {
        switch err.(type) {
        case *exec.ExitError:
            return result, nil
        default:
            return "", nil
        }
    }
    return result, nil
}

func echoString(str string) string {
    return fmt.Sprintf(`<( echo -e "%s" )`, strings.Replace(str, `"`, `\"`, -1))
}

There is no output at all and I get diff: missing operand after `diff' diff: Try `diff --help' for more information. in stderr.

So I thought I did not really need the echo instructions because I already got the strings, so I tried to replace echoString implementation with just the escape part, i.e. return strings.Replace(str, `"`, `\"`, -1) but I get the same error.

Any ideas?

Answer 1

Here is simplest solution, just pass diff command to bash shell:

    cmd := exec.Command(
        "bash", "-c", 
        fmt.Sprintf("diff <(echo -e %s) <(echo -e %s)", str1, str2))