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PIPE(3P)                   POSIX Programmer's Manual                  PIPE(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       pipe -- create an interprocess channel
SYNOPSIS
       #include <unistd.h>
       int pipe(int fildes[2]);
DESCRIPTION
       The pipe() function shall create a pipe and place two file descriptors,
       one  each into the arguments fildes[0] and fildes[1], that refer to the
       open file descriptions for the read and write ends of the  pipe.  Their
       integer  values  shall  be  the two lowest available at the time of the
       pipe() call. The O_NONBLOCK and FD_CLOEXEC flags shall be clear on both
       file  descriptors.  (The fcntl() function can be used to set both these
       flags.)
       Data can be written to the file descriptor fildes[1] and read from  the
       file  descriptor  fildes[0].   A  read on the file descriptor fildes[0]
       shall access data written to the file descriptor fildes[1] on a  first-
       in-first-out  basis.  It  is unspecified whether fildes[0] is also open
       for writing and whether fildes[1] is also open for reading.
       A process has the pipe open for reading (correspondingly writing) if it
       has  a  file  descriptor  open  that  refers to the read end, fildes[0]
       (write end, fildes[1]).
       The pipe's user ID shall be set to the effective user ID of the calling
       process.
       The pipe's group ID shall be set to the effective group ID of the call-
       ing process.
       Upon successful completion, pipe() shall mark for update the last  data
       access,  last data modification, and last file status change timestamps
       of the pipe.
RETURN VALUE
       Upon successful completion, 0 shall be returned; otherwise, -1 shall be
       returned and errno set to indicate the error.
ERRORS
       The pipe() function shall fail if:
       EMFILE All,  or  all  but one, of the file descriptors available to the
              process are currently open.
       ENFILE The number of simultaneously open  files  in  the  system  would
              exceed a system-imposed limit.
       The following sections are informative.
EXAMPLES
   Using a Pipe to Pass Data Between a Parent Process and a Child Process
       The  following  example demonstrates the use of a pipe to transfer data
       between a parent  process  and  a  child  process.  Error  handling  is
       excluded, but otherwise this code demonstrates good practice when using
       pipes: after the fork() the two processes close the unused ends of  the
       pipe before they commence transferring data.
           #include <stdlib.h>
           #include <unistd.h>
           ...
           int fildes[2];
           const int BSIZE = 100;
           char buf[BSIZE];
           ssize_t nbytes;
           int status;
           status = pipe(fildes);
           if (status == -1 ) {
               /* an error occurred */
               ...
           }
           switch (fork()) {
           case -1: /* Handle error */
               break;
           case 0:  /* Child - reads from pipe */
               close(fildes[1]);                       /* Write end is unused */
               nbytes = read(fildes[0], buf, BSIZE);   /* Get data from pipe */
               /* At this point, a further read would see end of file ... */
               close(fildes[0]);                       /* Finished with pipe */
               exit(EXIT_SUCCESS);
           default:  /* Parent - writes to pipe */
               close(fildes[0]);                       /* Read end is unused */
               write(fildes[1], "Hello world\n", 12);  /* Write data on pipe */
               close(fildes[1]);                       /* Child will see EOF */
               exit(EXIT_SUCCESS);
           }
APPLICATION USAGE
       None.
RATIONALE
       The  wording  carefully  avoids  using the verb ``to open'' in order to
       avoid any implication of use of open(); see also write().
FUTURE DIRECTIONS
       None.
SEE ALSO
       fcntl(), read(), write()
       The Base Definitions volume of POSIX.1-2008, <fcntl.h>, <unistd.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                             PIPE(3P)