pipe(3p) [suse man page]

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 correspond-
       ing 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]).

       Upon successful completion, pipe() shall mark for update the st_atime, st_ctime, and st_mtime fields 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 More than {OPEN_MAX} minus two file descriptors are already in use by this process.

       ENFILE The number of simultaneously open files in the system would exceed a system-imposed limit.

       The following sections are informative.

EXAMPLES

       None.

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 IEEE Std 1003.1-2001, <fcntl.h>, <unistd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								  PIPE(3P)

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 correspond-
       ing 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 calling process.

       Upon successful completion, pipe() shall mark for update the last data access, last data modification, and last file  status  change  time-
       stamps 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
", 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 Technol-
       ogy -- 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 Stan-
       dard 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)