How to print buffer to stdout but also capture as string?

Question

I know how to capture the output of a exec.Command but I would like to also stream it to stdout while still capturing it. Thanks for any input!

package main

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

func main() {
    cmd := exec.Command("ls")
    var out bytes.Buffer
    cmd.Stdout = &out
    cmd.Run()
    fmt.Println(out.String())
}

Either using io.TeeReader() or io.MultiWriter(). For an example, see What is the difference between io.TeeRearder and io.Copy? — icza
– icza, Commented Apr 13, 2022 at 14:23
ls may be a toy example here. But if not, it's preferred to use native Go APIs (like os.ReadDir) rather than launching an external executable. — colm.anseo
– colm.anseo, Commented Apr 13, 2022 at 14:48

Chandan · Accepted Answer · 2022-04-15 10:01:28Z

3

Example using `io.MultiWriter`

package main

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

func main() {
    cmd := exec.Command("ls")
    var out bytes.Buffer
    w := io.MultiWriter(os.Stdout, &out)
    cmd.Stdout = w
    fmt.Printf("===Stdout:===\n")
    cmd.Run()
    fmt.Printf("\n===Variable:===\n")
    fmt.Println(out.String())
}

edited Apr 15, 2022 at 10:01

answered Apr 15, 2022 at 6:31

Chandan

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How to print buffer to stdout but also capture as string?

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Example using `io.MultiWriter`

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Example using `io.MultiWriter`