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