gno/usr.man/man2/pipe.2

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.\"     @(#)pipe.2	8.1 (Berkeley) 6/4/93
.\"
.TH PIPE 2 "16 January 1997" GNO "System Calls"
.SH NAME
.BR pipe
\- create descriptor pair for interprocess communication
.SH SYNOPSIS
.br
#include <unistd.h>
.sp 1
int
\fBpipe\fR (int *\fIfildes\fR);
.SH DESCRIPTION
The
.BR pipe 
function
creates a
.IR pipe ,
which is an object allowing
unidirectional data flow,
and allocates a pair of file descriptors.
The first descriptor connects to the
.IR read
end of the pipe,
and the second connects to the
.IR write
end, so that data written to
.I fildes[1]
appears on (i.e., can be read from)
.IR 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.
.LP
A pipe whose read or write end has been closed is considered
.IR widowed .
Writing on such a pipe causes the writing process to receive
a
.BR 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 (end of file).
.SH LIMITS
Up to 4096 bytes of data are buffered before the writing process is
suspended.  Should more than 4096 bytes be necessary in any pipe among
a loop of processes, deadlock will occur.  This is not a limitation
specific to GNO but to multiprogramming in general.
.SH NOTES
This man page refers to the Unix
.BR read (2)
and 
.BR write (2)
operations.  On the IIgs, the described behavior refer to any system
calls doing I/O, including:
.RS
.nf
GS/OS ReadGS and WriteGS
TextTools calls
C stdio I/O routines
.fi
.RE
.SH RETURN VALUES
On successful creation of the pipe, zero is returned. Otherwise, 
a value of -1 is returned and the variable
.IR errno
set to indicate the
error.
.SH ERRORS
The
.BR pipe 
call will fail if:
.RS
.IP \fBEMFILE\fR
Too many descriptors are active.
.IP \fBENFILE\fR
The system file table is full.
.IP \fBEFAULT\fR
The
.I fildes
buffer is in an invalid area of the process's address
space.
.RE
.SH SEE ALSO
.BR sh (1),
.BR read (2),
.BR write (2),
.BR fork (2),
.BR socketpair (2)
.SH HISTORY
A
.BR pipe
function call appeared in Version 6 AT&T UNIX.