Context: I am trying to write a small tool in Golang, which spawns a vim editor and tries to record all the keystrokes input by the user.

package main

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

func main() {
    cmd := exec.Command("vim", "test.txt")

    rdr := bufio.NewReader(os.Stdin)

    cmd.Stdin = rdr
    cmd.Stdout = os.Stdout
    if err := cmd.Run(); err != nil {
        fmt.Println("err", err)
        return
    }
}

The above piece of code works as expected, but I want to record the keystrokes into a temporary buffer, for this I am using an io.TeeReader which writes the os.Stdin contents into a bytes.Buffer. This seems to break the tty and vim starts behaving weirdly and doesn’t differentiate between the insert mode and command mode.

Example code:

package main

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

func main() {
    cmd := exec.Command("vim", "test.txt")

    vimBuff := bytes.Buffer{}
    rdr := io.TeeReader(os.Stdin, &vimBuff)

    cmd.Stdin = rdr
    cmd.Stdout = os.Stdout
    if err := cmd.Run(); err != nil {
        fmt.Println("err", err)
        return
    }
}