NAME
pipe —
create descriptor pair for interprocess
communication
SYNOPSIS
#include
<unistd.h>
int
pipe(int
fildes[2]);
DESCRIPTION
The
pipe()
function creates a pipe, which is an object allowing
unidirectional data flow, and allocates a pair of file descriptors. The
first descriptor connects to the
read end
of the pipe, and the second connects to the
write
end, so that data written to fildes[1] appears
on (i.e., can be read from) fildes[0]. This allows the
output of one program to be sent to another program: the source's standard
output is set up to be the write end of the pipe, and the sink's standard
input is set up to be the read end of the pipe. The pipe itself persists
until all its associated descriptors are closed.
A pipe whose read or write end has been closed is
considered
widowed. Writing
on such a pipe causes the writing process to receive a
SIGPIPE signal. Widowing a pipe is the only way to
deliver end-of-file to a reader: after the reader consumes any buffered
data, reading a widowed pipe returns a zero count.
RETURN VALUES
On successful creation of the pipe, zero is returned. Otherwise, a value of -1 is returned and the variable errno set to indicate the error.
ERRORS
The pipe() call will fail if:
- [
EMFILE] - Too many descriptors are active.
- [
ENFILE] - The system file table is full.
- [
EFAULT] - The fildes buffer is in an invalid area of the process's address space.
SEE ALSO
STANDARDS
The pipe() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”).
As an extension, the pipe provided is actually capable of moving data bidirectionally. This is compatible with SVR4. However, this is non-POSIX behaviour which should not be relied on, for reasons of portability.
HISTORY
A pipe() function call appeared in
Version 3 AT&T UNIX. Since
Version 4 AT&T UNIX, it allocates two
distict file descriptors.