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PIPE(3P) POSIX Programmer's Manual PIPE(3P)
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.
pipe — create an interprocess channel
#include <unistd.h>
int pipe(int fildes[2]);
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.
Upon successful completion, 0 shall be returned; otherwise, −1 shall
be returned and errno set to indicate the error.
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.
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);
}
None.
The wording carefully avoids using the verb ``to open'' in order to
avoid any implication of use of open(); see also write().
None.
fcntl(3p), read(3p), write(3p)
The Base Definitions volume of POSIX.1‐2008, fcntl.h(0p),
unistd.h(0p)
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)
Pages that refer to this page: stropts.h(0p), unistd.h(0p), sh(1p), fstatvfs(3p), ioctl(3p), popen(3p), read(3p), system(3p), write(3p)