A pipe 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.
A FIFO special file 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.
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
SIGPIPE signal, and fails with error code EPIPE if the
signal is handled or blocked.
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.
