Go lang convert os.File output to String

Question

How to convert Os.File output into string instead of printing to shell. I am using github.com/kr/pty library to execute commands.

How can convert the output to sting instead of printing to console.

f belongs to Os.File in below example. How to convert it to string.

package main

import (
    "github.com/kr/pty"
    "io"
    "os"
    "os/exec"
)

func run_command(cmd string){
    c := exec.Command("/bin/sh", "-c", cmd)
    f, err := pty.Start(c)
    if err != nil {
        panic(err)
    }
    io.Copy(os.Stdout, f)
}

func main() {
    run_command("ls -lrt");
}

kr/pty writes to the terminal, that's actually the whole point of it. If you just want the program's stdout, you should use os/exec directly. It even has an example to show you how, you just need to string(out) on the resulting []byte. — Marc
– Marc, Commented Feb 3, 2018 at 10:35
If you really want to re-read the file (assuming it's an actual file, but I believe kr/pty writes to the console, so there's nothing to read back), you can always use ioutil.ReadAll on the *os.File. But again: the file pty opens is a terminal file descriptor, it just displays the contents, you don't be able to read them back. — Marc
– Marc, Commented Feb 3, 2018 at 10:43

AnhellO · Accepted Answer · 2024-02-02 07:11:27Z

4

Instead of

io.Copy(os.Stdout, f)

you can do

var buf bytes.Buffer
io.Copy(&buf, f)
asString := buf.String()

edited Feb 2, 2024 at 7:11

AnhellO

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answered Sep 22, 2018 at 14:20

gonutz

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Comments

3 revs user12258482 · Accepted Answer · 2022-03-08 01:01:15Z

2

An *os.File is an io.Reader. There are a few ways to convert the contents of an io.Reader to a string using the standard library.

The strings.Builder approach might perform better than the other approaches because strings.Builder does not allocate memory when converting the accumulated bytes to a string. This performance benefit is probably negligible in the context of the question.

Otherwise, the choice of approach is a matter of taste and opinion.

strings.Builder

var buf strings.Builder
_, err := io.Copy(&buf, f)
if err != nil {
    // handle error
}
s := buf.String()

bytes.Buffer

var buf bytes.Buffer
_, err := buf.ReadFrom(f)
if err != nil {
    // handle error
}
s := buf.String()

ioutil.ReadAll

p, err := ioutil.ReadAll(f)
if err != nil {
     // handle error
}
s := string(p)

edited Mar 8, 2022 at 1:01

community wiki

3 revs
user12258482

1 Comment

Nathan Boaldin Over a year ago

Does ioutil.Read need to be ioutil.ReadAll?

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