pipe.2 (2010 09)

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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 (see streampipes (5)) 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);
/* check process id of child process */
if ((pid = fork()) == (pid_t)0) {
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
pipe() returns one of the following values:
0 Successful completion.
-1 Failure. errno is set to indicate the error.
ERRORS
pipe() sets errno to one of the following error values if the corresponding condition is true.
[EMFILE]
NFILE-1 or more file descriptors are currently open.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1