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.
ENFILE: The system file table is full.
ENOSPC: The file system lacks sufficient space to create the pipe.
ENOSR: Could not allocate resources for both Stream heads (STREAMS-based pipes only).

STANDARDS CONFORMANCE

pipe(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1

pipe(2)

Technical documentation

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