[unix-history] / .ref-8c8a5b54e79564c14fc7a2823a21a8f048449bcf / usr / src / lib / libc / sys / pipe.2

.\" Copyright (c) 1980, 1991 Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.man%
.\"
.\"     @(#)pipe.2	6.3 (Berkeley) %G%
.\"
.Dd 
.Dt PIPE 2
.Os BSD 4
.Sh NAME
.Nm pipe
.Nd create descriptor pair for interprocess communication
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn pipe "int *fildes"
.Sh DESCRIPTION
The
.Fn pipe
function
creates a
.Em pipe ,
which is an object allowing
unidirectional data flow,
and allocates a pair of file descriptors.
The first descriptor connects to the
.Em read end
of the pipe,
and the second connects to the
.Em write end  ,
so that data written to
.Fa fildes[1]
appears on (i.e., can be read from)
.Fa 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.
.Pp
A pipe whose read or write end has been closed is considered
.Em widowed .
Writing on such a pipe causes the writing process to receive
a
.Dv 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.
.Pp
Pipes are really a special case of the 
.Xr socketpair 2
call and, in fact, are implemented as such in the system.
.Sh RETURN VALUES
On successful creation of the pipe, zero is returned. Otherwise, 
a value of -1 is returned and the variable
.Va errno
set to indicate the
error.
.Sh ERRORS
The
.Fn pipe
call will fail if:
.Bl -tag -width [EMFILE]
.It Bq Er EMFILE
Too many descriptors are active.
.It Bq Er ENFILE
The system file table is full.
.It Bq Er EFAULT
The
.Fa fildes
buffer is in an invalid area of the process's address
space.
.El
.Sh SEE ALSO
.Xr sh 1 ,
.Xr read 2 ,
.Xr write 2 ,
.Xr fork 2 ,
.Xr socketpair 2
.Sh HISTORY
A
.Nm
function call appeared in Version 6 AT&T UNIX.
Commit	Line	Data
931b8415 CL	1	.\" Copyright (c) 1980, 1991 Regents of the University of California.
931b8415 CL	2	.\" All rights reserved.
c15b236d	3	.\"
931b8415	4	.\" %sccs.include.redist.man%
c15b236d	5	.\"
931b8415 CL	6	.\" @(#)pipe.2 6.3 (Berkeley) %G%
	7	.\"
	8	.Dd
	9	.Dt PIPE 2
	10	.Os BSD 4
	11	.Sh NAME
	12	.Nm pipe
	13	.Nd create descriptor pair for interprocess communication
	14	.Sh SYNOPSIS
	15	.Fd #include <unistd.h>
	16	.Ft int
	17	.Fn pipe "int *fildes"
	18	.Sh DESCRIPTION
c15b236d	19	The
931b8415 CL	20	.Fn pipe
	21	function
	22	creates a
	23	.Em pipe ,
	24	which is an object allowing
	25	unidirectional data flow,
	26	and allocates a pair of file descriptors.
	27	The first descriptor connects to the
	28	.Em read end
	29	of the pipe,
	30	and the second connects to the
	31	.Em write end ,
	32	so that data written to
	33	.Fa fildes[1]
	34	appears on (i.e., can be read from)
	35	.Fa fildes[0] .
	36	This allows the output of one program to be
	37	sent
	38	to another program:
	39	the source's standard output is set up to be
	40	the write end of the pipe,
	41	and the sink's standard input is set up to be
	42	the read end of the pipe.
	43	The pipe itself persists until all its associated descriptors are
	44	closed.
	45	.Pp
	46	A pipe whose read or write end has been closed is considered
	47	.Em widowed .
	48	Writing on such a pipe causes the writing process to receive
	49	a
	50	.Dv SIGPIPE
	51	signal.
	52	Widowing a pipe is the only way to deliver end-of-file to a reader:
	53	after the reader consumes any buffered data, reading a widowed pipe
	54	returns a zero count.
	55	.Pp
0bbf2c7d	56	Pipes are really a special case of the
931b8415	57	.Xr socketpair 2
0bbf2c7d	58	call and, in fact, are implemented as such in the system.
931b8415 CL	59	.Sh RETURN VALUES
	60	On successful creation of the pipe, zero is returned. Otherwise,
	61	a value of -1 is returned and the variable
	62	.Va errno
	63	set to indicate the
	64	error.
	65	.Sh ERRORS
	66	The
	67	.Fn pipe
	68	call will fail if:
	69	.Bl -tag -width [EMFILE]
	70	.It Bq Er EMFILE
0bbf2c7d	71	Too many descriptors are active.
931b8415	72	.It Bq Er ENFILE
fd690c8b	73	The system file table is full.
931b8415 CL	74	.It Bq Er EFAULT
	75	The
	76	.Fa fildes
	77	buffer is in an invalid area of the process's address
0bbf2c7d	78	space.
931b8415 CL	79	.El
	80	.Sh SEE ALSO
	81	.Xr sh 1 ,
	82	.Xr read 2 ,
	83	.Xr write 2 ,
	84	.Xr fork 2 ,
	85	.Xr socketpair 2
	86	.Sh HISTORY
	87	A
	88	.Nm
	89	function call appeared in Version 6 AT&T UNIX.