NAME

       pipe, pipe2 — create descriptor pair for interprocess communication

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <unistd.h>

       int
       pipe(int fildes[2]);

       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.

IMPLEMENTATION NOTES

       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().

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:

       [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.

SEE ALSO

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

HISTORY

       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.

Debian                                          December 1, 2017                                         PIPE(2)