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



NAME
       pipe, pipe2 - create pipe

SYNOPSIS
       #include <unistd.h>

       int pipe(int pipefd[2]);

       #define _GNU_SOURCE
       #include <unistd.h>

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

DESCRIPTION
       pipe() creates a pipe, a unidirectional data channel that can be used for interpro-
       cess communication.  The array pipefd is used to return two file descriptors refer-
       ring  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 descrip-
                   tions.  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 descrip-
                   tors.  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 appropri-
       ately.

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 <assert.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;

           assert(argc == 2);

           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 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2008-11-04                           PIPE(2)

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