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PIPE(2)                  DragonFly System Calls Manual                 PIPE(2)


NAME

     pipe, pipe2 -- create descriptor pair for interprocess communication


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <unistd.h>

     int
     pipe(int *fildes);

     int
     pipe2(int fildes[2], int flags);


DESCRIPTION

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

     The pipe2() system call allows control over the attributes of the file
     descriptors via the flags argument.  Values for flags are constructed by
     a bitwise-inclusive OR of flags from the following list, defined in
     <fcntl.h>:

     O_CLOEXEC   Set the close-on-exec flag for the new file descriptors.

     O_NONBLOCK  Set the non-blocking flag for the ends of the pipe.

     If the flags argument is 0, the behavior is identical to a call to
     pipe().

     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
     direction.


RETURN VALUES

     The pipe() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.


ERRORS

     The pipe() and pipe2() system calls 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 address space.

     The pipe2() system call will also fail if:

     [EINVAL]           The flags argument is invalid.


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 Release 4 UNIX.

DragonFly 4.3                    June 4, 1993                    DragonFly 4.3

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