exec.Command sample code for show the stderr too

[dlin]

I've searched this group.  But, there are old samples.  And as I know exec.Command now return one argument.

When I execute "gnuplot tmp.gnuplot" on bash, it returns:

"tmp.gnuplot", line 25: warning: Skipping unreadable file "$1"

"tmp.gnuplot", line 25: warning: Skipping unreadable file "$1"

"tmp.gnuplot", line 25: No data in plot

But, when I execute my code, it returns:

2011/10/26 15:17:35 exit status 1

my code

=======

func plot() {

scriptName := "tmp.gnuplot"

cmd := exec.Command("gnuplot", scriptName)

bs, err := cmd.Output()

if err != nil { log.Fatalln(err) }

fmt.Println(bs)

}

[roger peppe]

On 26 October 2011 08:21, dlin <dli...@gmail.com> wrote:
> I've searched this group.  But, there are old samples.  And as I know
> exec.Command now return one argument.
> When I execute "gnuplot tmp.gnuplot" on bash, it returns:
> "tmp.gnuplot", line 25: warning: Skipping unreadable file "$1"
> "tmp.gnuplot", line 25: warning: Skipping unreadable file "$1"
> "tmp.gnuplot", line 25: No data in plot
> But, when I execute my code, it returns:
> 2011/10/26 15:17:35 exit status 1

i think you probably want to use CombinedOutput rather
than Output - the messages that gnuplot is printing
are being sent to stderr, which is directed to /dev/null by
default.

[Sebastien Binet]

see:
https://bitbucket.org/binet/go-gnuplot/src/ba2c342cf191/pkg/gnuplot/gnuplot.go#cl-51

my simple minded attempt at providing gnuplot commands from go.
I accept patches and push requests :)

-s

[dlin]

Sebastien, thanks.

I read the tutorial and  works.

[Robert Bloomquist]

Alternatively, you could connect gnuplot's standard error and standard output to the terminal's standard error and standard output:

func plot() {

scriptName := "tmp.gnuplot"

cmd := exec.Command("gnuplot", scriptName)

        cmd.Stdout = os.Stdout

        cmd.Stderr = os.Stderr

if err := cmd.Run(); err != nil { log.Fatalln(err) }

}

[dlin]

I'm wonder why CombinedOutput() failed, I think it may be a bug.

cmd := exec.Command("gnuplot", scriptname)

------------------

// workable code

        cmd.Stdout = os.Stdout

        cmd.Stderr = os.Stderr

if err := cmd.Run(); err != nil { log.Fatalln(err) }

// FAIL code

bs, e := cmd.CombinedOutput()

if e != nil {

log.Fatalln(e)

}

------------------

fmt.Println(string(bs))

[roger peppe]

it would be helpful if you could post a complete (small) example
that fails for you, as well as the error message that it gives.
otherwise we're left guessing!

[dlin]

Sorry, I've posted, but maybe not clearer.

result list here:

$ ./ok 

Cannot open load file 'wrong_file_name'

line 0: util.c: No such file or directory

2011/10/30 23:38:36 exit status 1

$ ./fail 

2011/10/30 23:38:38 exit status 1

// ok.go

func main() {

cmd := exec.Command("gnuplot", "wrong_file_name")

cmd.Stdout = os.Stdout

cmd.Stderr = os.Stderr

if err := cmd.Run(); err != nil {

log.Fatalln(err)

}

}

//fail.go

func main() {

cmd := exec.Command("gnuplot", "wrong_file_name")

bs, e := cmd.CombinedOutput()

if e != nil {

log.Fatalln(e)

}

fmt.Println(string(bs))

}

[John Asmuth]

What happens if you print bs before log.Fatalln()ing?

gnuplut might be returning an error code, which turns into an err that is not nil.

log.Fatal() exits the program and bs won't be printed.

[dlin]

Thanks, John, you solved my question.