[Main]

Pipe System Call

 #include <unistd.h>

     int
     pipe(int *fildes)

DESCRIPTION

     The pipe() function creates a pipe, which is an object allowing bidirec-
     tional data flow, and allocates a pair of file descriptors.

     By convention, the first descriptor is normally used as the read end of
     the pipe, and the second is normally the write end, so that data written
     to fildes[1] appears on (i.e., can be read from) fildes[0]. This allows
     the output of one program to be sent to another program: the source's
     standard output is set up to be the write end of the pipe, and the sink's
     standard input is set up to be the read end of the pipe.  The pipe itself
     persists until all its associated descriptors are closed.

     A pipe that has had an end closed is considered widowed. Writing on such
     a pipe causes the writing process to receive a SIGPIPE signal.  Widowing
     a pipe is the only way to deliver end-of-file to a reader: after the
     reader consumes any buffered data, reading a widowed pipe returns a zero
     count.

     The bidirectional nature of this implementation of pipes is not portable
     to older systems, so it is recommended to use the convention for using
     the endpoints in the traditional manner when using a pipe in one direc-
     tion.

RETURN VALUES

     On successful creation of the pipe, zero is returned. Otherwise, a value
     of -1 is returned and the variable errno set to indicate the error.

ERRORS

     The pipe() call will fail if:

     [EMFILE]  Too many descriptors are active.

     [ENFILE]  The system file table is full.

     [EFAULT]  The fildes buffer is in an invalid area of the process's ad-
	       dress space.

SEE ALSO

     sh(1),  fork(2),  read(2),  socketpair(2),  write(2)

HISTORY

     A pipe() function call appeared in Version 3 AT&T UNIX.

     Bidirectional pipes were first used on AT&T System V.4 UNIX.