HP-UX Reference (11i v2 07/12) - 2 System Calls (vol 5)

p
pipe(2) pipe(2)
NAME
pipe() - create an interprocess channel
SYNOPSIS
int pipe(int fildes[2]);
DESCRIPTION
pipe() creates an I/O mechanism called a pipe and returns two file descriptors, fildes[0] and fildes[1].
fildes[0] is opened for reading and fildes[1] is opened for writing.
A read-only file descriptor fildes[0] accesses the data written to fildes[1] on a first-in-first-out (FIFO) basis.
For details of the I/O behavior of pipes see read(2) and write(2).
By default, HP-UX pipes are not STREAMS-based. It is possible to generate the kernel so that all pipes
created on a system are STREAMS-based. This can only be done for HP-UX releases 10.0 and later.
STREAMS-based FIFOs (created by
mknod or mkfifo) are not supported on HP-UX.
To generate a kernel that supports STREAMS-based pipes:
• STREAMS/UX must be installed.
• The module
pipemod and the driver pipedev must be included in the /stand/system
file.
(When STREAMS/UX is installed,
pipemod and pipedev are automatically added to the system
file.)
• The tunable parameter "streampipes" must be set to 1 in the
/stand/system file. (This is not
automatically done when STREAMS/UX is installed.)
• The kernel must be generated and the system rebooted. Once this is done, all pipes created by
pipe() will be STREAMS-based.
For more information, see STREAMS/UX for the HP 9000 Reference Manual.
EXAMPLES
The following example uses
pipe() to implement the command string ls | sort:
#include <sys/types.h>
pid_t pid;
int pipefd[2];
/* Assumes file descriptor 0 and 1 are open */
pipe (pipefd);
if ((pid = fork()) == (pid_t)0) /* check process id of child process */ {
close(1); /* close stdout */
dup (pipefd[1]); /* points pipefd at file descriptor */
close (pipefd[0]);
execlp ("ls", "ls", (char *)0); /* child process does ls */
}
else if (pid > (pid_t)0) {
close(0); /* close stdin */
dup (pipefd[0]);
/* point the child’s standard output to parent’s standard input */
close (pipefd[1]);
execlp ("sort", "sort", (char *)0); /* parent process does sort */
}
RETURN VALUE
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is
set to indicate the error.
ERRORS
pipe() fails if one or more of the following is true:
[EMFILE] NFILE -1 or more file descriptors are currently open.
[ENFILE] The system file table is full.
HP-UX 11i Version 2: December 2007 Update − 1 − Hewlett-Packard Company 249