Index for Section 2

Alphabetical listing for P

Bottom of page

pipe(2)
NAME
  pipe - Create an interprocess channel

SYNOPSIS
  #include <unistd.h>

  int pipe(
	  int filedes[2] );

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  pipe(): XSH4.0, XSH4.2, XSH5.0

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  filedes Specifies the address of an array of two integers into which the
	  new file descriptors are placed.

DESCRIPTION
  The pipe() function creates a unidirectional interprocess channel called a
  pipe, and returns two file descriptors, filedes[0] and filedes[1]. The file
  descriptor specified by the filedes[0] parameter is opened for reading and
  the file descriptor specified by the filedes[1] parameter is opened for
  writing. Their integer values will be the two lowest available at the time
  of the call to the pipe() function.

  A process has the pipe open for reading if it has a file descriptor open
  that refers to the read end, filedes[0]. A process has the pipe open for
  writing if it has a file descriptor open that refers to the write end,
  filedes[1]. A read operation on file descriptor filedes[0] accesses the
  data written to filedes[1] on a first-in, first-out (FIFO) basis.

				     Note

       In the System V compatiblity environment, filedes[0] and filedes[1]
       are STREAMS based and are bidirectional.	 Data written on filedes[0]
       appears on filedes[1] and vice versa. Data is read in a first-in,
       first-out (FIFO) basis.

  The O_NONBLOCK and the FD_CLOEXC flags are set clear on both file
  descriptors. (The fcntl() function can be used to set the O_NONBLOCK flag.)

  Upon successful completion, the pipe() function marks the st_atime,
  st_ctime and st_mtime fields of the pipe for update.

NOTES
  [Tru64 UNIX]	When a read() or write() system call on a pipe is interrupted
  by a signal and no bytes have been transferred through the pipe, the read()
  or write() system call returns a -1 and errno is set to [EINTR]. This
  behavior differs from behavior in early releases of the operating system,
  when both system calls either restarted the transfer or caused errno to be
  set to [EINTR], depending on the setting of the SA_RESTART flag for the
  interrupting signal.

  [Tru64 UNIX]	As a result of this change, applications must now either
  handle the [EINTR] return or block any expected signals for the duration of
  the read or write operation.

  [Tru64 UNIX]	When compiled in the X/Open UNIX environment, calls to the
  pipe() function are internally renamed by prepending _E to the function
  name. When you are debugging a module that includes the pipe() function and
  for which _XOPEN_SOURCE_EXTENDED has been defined, use _Epipe to refer to
  the pipe() call.  See standards(5) for further information.

RETURN VALUES
  Upon successful completion, a value of 0 (zero) is returned. If the pipe()
  function fails, a value of -1 is returned and errno is set to indicate the
  error.

ERRORS
  If the pipe() function fails, errno may be set to one of the following
  values:

  [EFAULT]
	  [Tru64 UNIX]	The filedes parameter is an invalid address.

  [EINTR] [Tru64 UNIX]	A read() or a write() call on a pipe is interrupted
	  by a signal and no bytes have been transferred through the pipe.

  [EMFILE]
	  More than OPEN_MAX-2 file descriptors are already opened by this
	  process.

	  [Tru64 UNIX]	More than getdtablesize(2) file descriptors are
	  already opened by this process.

  [ENFILE]
	  The system file table is full, or the device containing pipes has
	  no free i-nodes.

  [ENOMEM]
	  [Tru64 UNIX]	The system was unable to allocate kernel memory for
	  more file descriptors.

SEE ALSO
  Commands: sh(1)

  Functions: fcntl(2), getmsg(2), getdtablesize(2), poll(2), putmsg(2),
  read(2), select(2), write(2)

  Standards: standards(5)

Index for Section 2

Alphabetical listing for P

Top of page