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diff --git a/share/doc/psd/20.ipctut/socketpair.c b/share/doc/psd/20.ipctut/socketpair.c
new file mode 100644
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+++ b/share/doc/psd/20.ipctut/socketpair.c
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+.\" Copyright (c) 1986, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" 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. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. 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 REGENTS 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 REGENTS 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.
+.\"
+.\"	@(#)socketpair.c	8.1 (Berkeley) 6/8/93
+.\"
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <stdio.h>
+
+#define DATA1 "In Xanadu, did Kublai Khan . . ."
+#define DATA2 "A stately pleasure dome decree . . ."
+
+/*
+ * This program creates a pair of connected sockets then forks and
+ * communicates over them.  This is very similar to communication with pipes,
+ * however, socketpairs are two-way communications objects. Therefore I can
+ * send messages in both directions. 
+ */
+
+main()
+{
+	int sockets[2], child;
+	char buf[1024];
+
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets) < 0) {
+		perror("opening stream socket pair");
+		exit(1);
+	}
+
+	if ((child = fork()) == -1)
+		perror("fork");
+	else if (child) {	/* This is the parent. */
+		close(sockets[0]);
+		if (read(sockets[1], buf, 1024, 0) < 0)
+			perror("reading stream message");
+		printf("-->%s\en", buf);
+		if (write(sockets[1], DATA2, sizeof(DATA2)) < 0)
+			perror("writing stream message");
+		close(sockets[1]);
+	} else {		/* This is the child. */
+		close(sockets[1]);
+		if (write(sockets[0], DATA1, sizeof(DATA1)) < 0)
+			perror("writing stream message");
+		if (read(sockets[0], buf, 1024, 0) < 0)
+			perror("reading stream message");
+		printf("-->%s\en", buf);
+		close(sockets[0]);
+	}
+}