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<!-- %MENU% A simple interprocess communication mechanism -->
<h2 class="chapter">15 Pipes and FIFOs</h2>

<p><a name="index-pipe-1614"></a>A <dfn>pipe</dfn> is a mechanism for interprocess communication; data written
to the pipe by one process can be read by another process.  The data is
handled in a first-in, first-out (FIFO) order.  The pipe has no name; it
is created for one use and both ends must be inherited from the single
process which created the pipe.

   <p><a name="index-FIFO-special-file-1615"></a>A <dfn>FIFO special file</dfn> is similar to a pipe, but instead of being an
anonymous, temporary connection, a FIFO has a name or names like any
other file.  Processes open the FIFO by name in order to communicate
through it.

   <p>A pipe or FIFO has to be open at both ends simultaneously.  If you read
from a pipe or FIFO file that doesn't have any processes writing to it
(perhaps because they have all closed the file, or exited), the read
returns end-of-file.  Writing to a pipe or FIFO that doesn't have a
reading process is treated as an error condition; it generates a
<code>SIGPIPE</code> signal, and fails with error code <code>EPIPE</code> if the
signal is handled or blocked.

   <p>Neither pipes nor FIFO special files allow file positioning.  Both
reading and writing operations happen sequentially; reading from the
beginning of the file and writing at the end.

<ul class="menu">
<li><a accesskey="1" href="Creating-a-Pipe.html#Creating-a-Pipe">Creating a Pipe</a>:              Making a pipe with the <code>pipe</code> function. 
<li><a accesskey="2" href="Pipe-to-a-Subprocess.html#Pipe-to-a-Subprocess">Pipe to a Subprocess</a>:         Using a pipe to communicate with a
				 child process. 
<li><a accesskey="3" href="FIFO-Special-Files.html#FIFO-Special-Files">FIFO Special Files</a>:           Making a FIFO special file. 
<li><a accesskey="4" href="Pipe-Atomicity.html#Pipe-Atomicity">Pipe Atomicity</a>: 		When pipe (or FIFO) I/O is atomic. 
</ul>

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