LinuxC选择:管道回音输入工作,但从键盘读取不工作?

我在试着理解 http://beej.us/guide/bgnet/examples/select.c (以下为参考)。我正在做:

:~$ cat /etc/issue

Ubuntu 10.04 LTS \n \l
:~$ gcc --version
gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3

:~$ wget http://beej.us/guide/bgnet/examples/select.c
:~$ gcc select.c -o select

:~$ echo "ff" | ./select 
A key was pressed!

:~$ ./select 
TYPINGTYTimed out.

因此,select程序显然可以将一个回音管道识别为输入;但它不能识别终端上的按键。这是为什么?是否可以使用某种重定向(我猜,类似于屏幕如何将键盘输入“重定向”到串行会话),以便识别终端中的实际按键?

谢谢, 干杯!

选择C:

/* ** select.c -- a select() demo */

#include <stdio.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

#define STDIN 0  // file descriptor for standard input

int main(void)
{
 struct timeval tv;
 fd_set readfds;

 tv.tv_sec = 2;
 tv.tv_usec = 500000;

 FD_ZERO(&readfds);
 FD_SET(STDIN, &readfds);

 // don't care about writefds and exceptfds:
 select(STDIN+1, &readfds, NULL, NULL, &tv);

 if (FD_ISSET(STDIN, &readfds))
  printf("A key was pressed!\n");
 else
  printf("Timed out.\n");

 return 0;
}

编辑:请参见答案,因此我们只需按回车键:

:~$ ./select 

A key was pressed!

:~ stty raw
:~ ./select 
                                            dA key was pressed!
                                                               :~ stty cooked