PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

PIPE(3P)                  POSIX Programmer's Manual                 PIPE(3P)

PROLOG         top

       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         top

       pipe — create an interprocess channel

SYNOPSIS         top

       #include <unistd.h>

       int pipe(int fildes[2]);

DESCRIPTION         top

       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
       calling 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         top

       Upon successful completion, 0 shall be returned; otherwise, −1 shall
       be returned and errno set to indicate the error.

ERRORS         top

       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         top

   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         top

       None.

RATIONALE         top

       The wording carefully avoids using the verb ``to open'' in order to
       avoid any implication of use of open(); see also write().

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       fcntl(3p), read(3p), write(3p)

       The Base Definitions volume of POSIX.1‐2008, fcntl.h(0p),
       unistd.h(0p)

COPYRIGHT         top

       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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                            PIPE(3P)