pipe(2) - f7

1PIPE(2)                    Linux Programmer's Manual                   PIPE(2)
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NAME

6       pipe - create pipe
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SYNOPSIS

9       #include <unistd.h>
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11       int pipe(int filedes[2]);
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DESCRIPTION

14       pipe()  creates  a  pair of file descriptors, pointing to a pipe inode,
15       and places them in the array pointed to by filedes.  filedes[0] is  for
16       reading, filedes[1] is for writing.
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RETURN VALUE

19       On  success,  zero is returned.  On error, -1 is returned, and errno is
20       set appropriately.
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ERRORS

23       EFAULT filedes is not valid.
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25       EMFILE Too many file descriptors are in use by the process.
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27       ENFILE The system limit on the total number  of  open  files  has  been
28              reached.
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CONFORMING TO

31       POSIX.1-2001.
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EXAMPLE

34       The  following  program  creates  a pipe, and then fork(2)s to create a
35       child process.  After the fork(2), each process closes the  descriptors
36       that  it  doesn't  need  for  the  pipe (see pipe(7)).  The parent then
37       writes the string contained in the program's command-line  argument  to
38       the  pipe,  and  the  child reads this string a byte at a time from the
39       pipe and echoes it on standard output.
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41       #include <sys/wait.h>
42       #include <assert.h>
43       #include <stdio.h>
44       #include <stdlib.h>
45       #include <unistd.h>
46       #include <string.h>
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48       int
49       main(int argc, char *argv[])
50       {
51           int pfd[2];
52           pid_t cpid;
53           char buf;
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55           assert(argc == 2);
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57           if (pipe(pfd) == -1) { perror("pipe"); exit(EXIT_FAILURE); }
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59           cpid = fork();
60           if (cpid == -1) { perror("fork"); exit(EXIT_FAILURE); }
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62           if (cpid == 0) {    /* Child reads from pipe */
63               close(pfd[1]);          /* Close unused write end */
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65               while (read(pfd[0], &buf, 1) > 0)
66                   write(STDOUT_FILENO, &buf, 1);
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68               write(STDOUT_FILENO, "\n", 1);
69               close(pfd[0]);
70               _exit(EXIT_SUCCESS);
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72           } else {            /* Parent writes argv[1] to pipe */
73               close(pfd[0]);          /* Close unused read end */
74               write(pfd[1], argv[1], strlen(argv[1]));
75               close(pfd[1]);          /* Reader will see EOF */
76               wait(NULL);             /* Wait for child */
77               exit(EXIT_SUCCESS);
78           }
79       }
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