os.Stdin is whatever the file descriptor 0 is being connected to by the OS.
Depending on the type of file descriptor, Read will behave differently. If
you call a program on the command line, the shell connects it to its
controlling terminal, which is usually line-buffered and a read from it
will block until a new line is written. If you pipe another command into
it, it will connect that program's stdout to your programs stdin and as
soon as that program (echo, in your example) finishes, a Read will return
io.EOF.
Note that this isn't really Go-specific. All languages will behave that way.
On Sun, Dec 12, 2021 at 5:16 PM Денис Мухортов <muhortovdeni...@gmail.com>
wrote:
> It's a little unclear how os.stdin actually works. Why, if you just run
> the program, is data from stdin constantly being listened to?
> For example:
> func main() {
> sc := bufio.NewScanner(os.Stdin)
> for sc.Scan() {
> txt := sc.Text()
> fmt.Printf("echo: %s\n", txt)
> }
> } But if you send it to stdin ahead of time, the loop will run once and
> the program will exit(echo smth | go run main.go)
>
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