CODEWITHSUNDEEP
go
Sławosz
Sławosz

Reputation: 11697

Strange behaviour of golang exec.Command program

I have such code:

func main() {
        s := "foobar"
        cmd := exec.Command("wc", "-l")
        stdin, err := cmd.StdinPipe()
        if err != nil {
                log.Panic(err)
        }
        stdout, err := cmd.StdoutPipe()
        if err != nil {
                log.Panic(err)
        }
        err = cmd.Start()
        if err != nil {
                log.Panic(err)
        }
        io.Copy(stdin, bytes.NewBufferString(s))
        stdin.Close()
        io.Copy(os.Stdout, stdout)
        err = cmd.Wait()
        if err != nil {
                log.Panic(err)
        }
}

and its output is:

0

But when I will do simple modification:

func main() {
        runWcFromStdinWorks("aaa\n")
        runWcFromStdinWorks("bbb\n")
}

func runWcFromStdinWorks(s string) {
        cmd := exec.Command("wc", "-l")
        stdin, err := cmd.StdinPipe()
        if err != nil {
                log.Panic(err)
        }
        stdout, err := cmd.StdoutPipe()
        if err != nil {
                log.Panic(err)
        }
        err = cmd.Start()
        if err != nil {
                log.Panic(err)
        }
        io.Copy(stdin, bytes.NewBufferString(s))
        stdin.Close()
        io.Copy(os.Stdout, stdout)
        err = cmd.Wait()
        if err != nil {
                log.Panic(err)
        }
}

It works, but why? Its just calling method why first version is not working?

Upvotes: 0

Views: 171

Answers (1)

Miki Tebeka
Miki Tebeka

Reputation: 13910

The string s in the first example does not have a new line, which causes wc -l to return 0. You can see this behavior by doing:

$ echo -n hello | wc -l
0

Upvotes: 4

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