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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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. The file descriptors shall be allocated as
described in Section 2.14, File Descriptor Allocation. 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, no file
descriptors shall be allocated and the contents of fildes shall
be left unmodified.
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.
Section 2.14, File Descriptor Allocation, fcntl(3p), read(3p),
write(3p)
The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
unistd.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 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)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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