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PIPE(2) 		       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[2]);

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

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

     The pipe2() system call allows control over the attributes of the file  de-
     scriptors	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_CLOFORK	 Set the close-on-fork 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.

     The O_CLOFORK flag appeared in FreeBSD 15.0.

FreeBSD ports 15.quarterly	  May 17, 2025				 PIPE(2)

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