V3/usr/man/man2/pipe.2

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including files from this version of Unix. 
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NAME		pipe -- create a pipe
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SYNOPSIS	sys pipe	/ pipe = 42.; not in assembler
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(file descriptor in r0)
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DESCRIPTION	The
pipe____
system call
creates an I/O mechanism called a pipe.
The file descriptor returned can
be used in both read and write operations.
When the pipe is written,
the data is buffered up to 504 bytes
at which time the writing process is suspended.
A read on the pipe will pick up the buffered data.
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It is assumed that after the
pipe____ has been set up,
two (or more)
cooperating processes
(created by subsequent fork____ calls)
will pass data through the
pipe with read____ and write_____ calls.

The shell has a syntax
to set up a linear array of processes
connected by pipes.
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Read calls on an empty
pipe (no buffered data) with only one end
(no synonymous file
descriptors resulting from fork____ or dup___)
return an end-of-file.
Write calls under similar conditions are ignored.

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SEE ALSO	sh(I), read(II), write(II), fork(II)
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DIAGNOSTICS	The error
bit (c-bit) is set if
10 files are already open.
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BUGS		--