PIPE(2)                      BSD System Calls Manual                     PIPE(2)

     pipe, pipe2 — create descriptor pair for interprocess communication

     Standard C Library (libc, -lc)

     #include <unistd.h>

     pipe(int fildes[2]);

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

     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

     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.

     The pipe() function calls the pipe2() system call.  As a result, system
     call traces such as those captured by dtrace(1) or ktrace(1) will show
     calls to pipe2().

     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

     The pipe() and pipe2() system calls will fail if:

     [EFAULT]           fildes argument points to an invalid memory location.

     [EMFILE]           Too many descriptors are active.

     [ENFILE]           The system file table is full.

     [ENOMEM]           Not enough kernel memory to establish a pipe.

     The pipe2() system call will also fail if:

     [EINVAL]           The flags argument is invalid.

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

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

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

     The pipe2() function appeared in FreeBSD 10.0.

     The pipe() function became a wrapper around pipe2() in FreeBSD 11.0.

BSD                             December 1, 2017                             BSD