• 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 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
  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

  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 3.19 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/.

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