<!-- Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009, 2013 The President and Fellows of Harvard College. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. --> <html> <head> <title>pipe</title> <body bgcolor=#ffffff> <h2 align=center>pipe</h2> <h4 align=center>OS/161 Reference Manual</h4> <h3>Name</h3> <p> pipe - create pipe object </p> <h3>Library</h3> <p> Standard C Library (libc, -lc) </p> <h3>Synopsis</h3> <p> <tt>#include <unistd.h></tt><br> <br> <tt>int</tt><br> <tt>pipe(int *</tt><em>fds</em><tt>);</tt> </p> <h3>Description</h3> <p> The <tt>pipe</tt> call creates an anonymous pipe object in the system, and binds it to two file handles in the current process, one for the read end and one for the write end. (Pipes are unidirectional.) </p> <p> Data written on the write end may be read from the read end. Once all references to the write end are closed, and all remaining data is read, further reads return EOF. If all references to the read end are closed before the write end is closed, further writes generate EPIPE. The pipe object itself is destroyed when all references to both ends are closed. </p> <p> <em>fds</em> is a pointer to space for two integers. A file handle for the read end of the pipe is stored in <em>fds</em>[0], and a file handle for the write end is stored in <em>fds</em>[1]. </p> <p> <tt>pipe</tt> is most often used in conjunction with <A HREF=dup2.html>dup2</A> and <A HREF=fork.html>fork</A> to send the standard output of one process to the standard input of another. </p> <p> In POSIX, pipe I/O of data blocks smaller than a standard constant PIPE_BUF is guaranteed to be atomic. If you implement pipes, you need not necessarily implement POSIX semantics, but you should decide what sort of atomicity guarantees you wish to make and specify them carefully. </p> <h3>Return Values</h3> <p> On success, pipe returns 0. On error, -1 is returned, and <A HREF=errno.html>errno</A> is set according to the error encountered. </p> <h3>Errors</h3> <p> The following error codes should be returned under the conditions given. Other error codes may be returned for other cases not mentioned here. <table width=90%> <tr><td width=5% rowspan=3> </td> <td width=10% valign=top>EMFILE</td> <td>The process's file table was full, or a process-specific limit on open files was reached.</td></tr> <tr><td valign=top>ENFILE</td> <td>The system file table is full, if such a thing exists, or a system-wide limit on open files was reached.</td></tr> <tr><td valign=top>EFAULT</td> <td><em>fds</em> was an invalid pointer.</td></tr> </table> </p> </body> </html>