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

       pipe, pipe2 - create pipe

       #include <unistd.h>

       int pipe(int pipefd[2]);

       #define _GNU_SOURCE
       #include <unistd.h>

       int pipe2(int pipefd[2], int flags);

       pipe()  creates  a  pipe,  a  unidirectional data channel that can be used for interprocess communication.  The
       array pipefd is used to return two file descriptors referring to the ends of the pipe.  pipefd[0] refers to the
       read  end  of  the  pipe.  pipefd[1] refers to the write end of the pipe.  Data written to the write end of the
       pipe is buffered by the kernel until it is read from the read end  of  the  pipe.   For  further  details,  see

       If flags is 0, then pipe2() is the same as pipe().  The following values can be bitwise ORed in flags to obtain
       different behavior:

       O_NONBLOCK  Set the O_NONBLOCK file status flag on the two new open file descriptions.  Using this  flag  saves
                   extra calls to fcntl(2) to achieve the same result.

       O_CLOEXEC   Set  the  close-on-exec  (FD_CLOEXEC) flag on the two new file descriptors.  See the description of
                   the same flag in open(2) for reasons why this may be useful.

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

       EFAULT pipefd is not valid.

       EINVAL (pipe2()) Invalid value in flags.

       EMFILE Too many file descriptors are in use by the process.

       ENFILE The system limit on the total number of open files has been reached.

       pipe2() was added to Linux in version 2.6.27; glibc support is available starting with version 2.9.

       pipe(): POSIX.1-2001.

       pipe2() is Linux-specific.

       The following program creates a pipe, and then fork(2)s to create a child process; the child inherits a  dupli-
       cate  set of file descriptors that refer to the same pipe.  After the fork(2), each process closes the descrip-
       tors that it doesn't need for the pipe (see pipe(7)).  The parent then writes the string contained in the  pro-
       gram's  command-line  argument  to the pipe, and the child reads this string a byte at a time from the pipe and
       echoes it on standard output.

       #include <sys/wait.h>
       #include <assert.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <string.h>

       main(int argc, char *argv[])
           int pipefd[2];
           pid_t cpid;
           char buf;

           assert(argc == 2);

           if (pipe(pipefd) == -1) {

           cpid = fork();
           if (cpid == -1) {

           if (cpid == 0) {    /* Child reads from pipe */
               close(pipefd[1]);          /* Close unused write end */

               while (read(pipefd[0], &buf, 1) > 0)
                   write(STDOUT_FILENO, &buf, 1);

               write(STDOUT_FILENO, "\n", 1);

           } else {            /* Parent writes argv[1] to pipe */
               close(pipefd[0]);          /* Close unused read end */
               write(pipefd[1], argv[1], strlen(argv[1]));
               close(pipefd[1]);          /* Reader will see EOF */
               wait(NULL);                /* Wait for child */

       fork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)

       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

Linux                             2008-11-04                           PIPE(2)