Communication with pipe

The primitive for creating a pipe is the `pipe' function.  This creates
both the reading and writing ends of the pipe.  It is not very useful
for a single process to use a pipe to talk to itself.  In typical use,
a process creates a pipe just before it forks one or more child
processes (*note Creating a Process::).  The pipe is then used for
communication either between the parent or child processes, or between
two sibling processes.
The file discriptor for reading pipe is [0]& for write [1].