.TH PIPE 3
.SH NAME
pipe \- create an interprocess channel
.SH SYNOPSIS
.B #include <u.h>
.br
.B #include <libc.h>
.PP
.B
int pipe(int fd[2])
.SH DESCRIPTION
.I Pipe
creates a buffered channel for interprocess I/O communication.
Two file descriptors are returned in
.IR fd .
Data written to
.B fd[1]
is available for reading from
.B fd[0]
and data written to
.B fd[0]
is available for reading from
.BR fd[1] .
.PP
After the pipe has been established,
cooperating processes
created by subsequent
.IR fork (3)
calls may pass data through the
pipe with
.I read
and
.I write
calls.
The bytes placed on a pipe
by one 
.I write
are contiguous even if many processes are writing.
Write boundaries are preserved: each read terminates
when the read buffer is full or after reading the last byte
of a write, whichever comes first.
.PP
The number of bytes available to a
.IR read (3)
is reported
in the
.B Length
field returned by
.I fstat
or
.I dirfstat
on a pipe (see
.IR stat (3)).
.PP
When all the data has been read from a pipe and the writer has closed the pipe or exited,
.IR read (3)
will return 0 bytes.  Writes to a pipe with no reader will generate a note
.BR "sys: write on closed pipe" .
.SH SOURCE
.B /sys/src/libc/9syscall
.SH SEE ALSO
.IR intro (3),
.IR read (3),
.IR pipe (3)
.SH DIAGNOSTICS
Sets
.IR errstr .
.SH BUGS
If a read or a write of a pipe is interrupted, some unknown
number of bytes may have been transferred.
.br
When a read from a pipe returns 0 bytes, it usually means end of file
but is indistinguishable from reading the result of an explicit
write of zero bytes.