C语言编程。 如何读取我的程序中来自另一个程序的输入（通过管道）？

Question

Here is what I try to run: (echo echo abc;echo echo def;echo echo ghi)|./myprogram

So input to myprogram comes from a pipe.

I am trying to read it as:

while (fgets(line, MAXLINE+1, stdin)){
...
}

But as I understand input that comes to my program is now stdin, right? So it does not work. I am not sure how to change my program so it works with input that is coming from another program.

Thank you!

Answer 1

What you posit is exactly how you should do it. By piping information into your program, it's mostly indistinguishable ^(a) from regular input, as the following transcript shows:

pax$ cat testprog.c
#include <stdio.h>
int main (void) {
        char line[1000];
        while (fgets (line, sizeof(line), stdin)) {
                printf ("%s", line);
        }
        return 0;
}

pax$ gcc -o testprog testprog.c

pax$ ( echo echo abc;echo echo def;echo echo ghi ) | ./testprog
echo abc
echo def
echo ghi

---

^(a) There are ways to tell, such as with isatty() but you have to expend some effort. Mostly, input from a file or pipe or device can be treated as if you were entering it on the keyboard yourself.