NAME

       pipe, pipe2 - create pipe

SYNOPSIS

       #include <unistd.h>

       int pipe(int pipefd[2]);

       #define _GNU_SOURCE             /* See feature_test_macros(7) */
       #include <fcntl.h>              /* Obtain O_* constant definitions */
       #include <unistd.h>

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

DESCRIPTION

       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 pipe(7).

       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.

RETURN VALUE

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

ERRORS

       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.

VERSIONS

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

CONFORMING TO

       pipe(): POSIX.1-2001.

       pipe2() is Linux-specific.

EXAMPLE

       The following program creates a pipe, and then fork(2)s to create a child process; the child  inherits  a
       duplicate  set  of  file descriptors that refer to the same pipe.  After the fork(2), each process closes
       the descriptors that it doesn't need for the pipe (see pipe(7)).   The  parent  then  writes  the  string
       contained in the program'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 <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <string.h>

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

           if (argc != 2) {
            fprintf(stderr, "Usage: %s <string>\n", argv[0]);
            exit(EXIT_FAILURE);
           }

           if (pipe(pipefd) == -1) {
               perror("pipe");
               exit(EXIT_FAILURE);
           }

           cpid = fork();
           if (cpid == -1) {
               perror("fork");
               exit(EXIT_FAILURE);
           }

           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);
               close(pipefd[0]);
               _exit(EXIT_SUCCESS);

           } 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 */
               exit(EXIT_SUCCESS);
           }
       }

SEE ALSO

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

COLOPHON

       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.