I/O重定向和管道

 1 #include <stdio.h>
 2 #include <stdlib.h>
 3 #include <string.h>
 4 #include <unistd.h>
 5 #include <fcntl.h>
 6 
 7 int main()
 8 {
 9     int len, i, apipe[2];
10     char buf[BUFSIZ];
11 
12     if (pipe(apipe) == -1)
13     {
14         perror("could not make pipe");
15         exit(1);
16     }
17 
18     printf("Got a pipe! It is file descriptors: {%d %d}\n", apipe[0], apipe[1]);
19 
20     int infd = open("/etc/passwd", O_RDONLY);
21     dup2(infd, 0);
22     int outfd = open("userlist", O_WRONLY);
23     dup2(outfd, 1);
24 
25 
26     while (fgets(buf, BUFSIZ, stdin))
27     {
28         len = strlen(buf);
29         if (write(apipe[1], buf, len) != len)
30         {
31             perror("writing to pipe");
32             break;
33         }
34 /*
35         for (i = 0; i < len; i++)
36         {
37             buf[i] = ‘X‘;
38         }
39 */
40         len = read(apipe[0], buf, BUFSIZ);
41         if (len == -1)
42         {
43             perror("reading from pipe");
44             break;
45         }
46         if (!fputs(buf, stdout))
47         {
48             perror("writing to stdout");
49             break;
50         }
51     }
52 
53     return 0;
54 }