pipe(2) System Calls Manual pipe(2)
pipe - Creates an interprocess channel
int pipe ( int filedes );
Interfaces documented on this reference page conform to industry standards as follows:
Refer to the standards(5) reference page for more information about industry standards and associated tags.
Specifies the address of an array of two integers into which the new file descriptors are placed.
The pipe() function creates a unidirectional interprocess channel called a pipe, and returns two file descriptors, filedes and
filedes. The file descriptor specified by the filedes parameter is opened for reading and the file descriptor specified by the
filedes parameter is opened for writing. Their integer values will be the two lowest available at the time of the call to the pipe()
A process has the pipe open for reading if it has a file descriptor open that refers to the read end, filedes. A process has the pipe
open for writing if it has a file descriptor open that refers to the write end, filedes. A read on file descriptor filedes accesses
the data written to filedes on a first-in, first-out (FIFO) basis.
System V Compatibility
The pipe() function creates an interprocess channel called a pipe and returns two file descriptors, filedes and filedes. Both file
descriptors are STREAMS based and are bidirectional. Data written on filedes appears on filedes and vice versa. Data is read in a
first-in, first-out (FIFO) basis.
Under both behaviors, 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.
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 is different from previous releases, 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
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.
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.
If the pipe() function fails, errno may be set to one of the following values: The filedes parameter is an invalid address. A read() or a
write() on a pipe is interrupted by a signal and no bytes have been transferred through the pipe. 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. The system file table is full, or the
device containing pipes has no free i-nodes. [Tru64 UNIX] The system was unable to allocate kernel memory for more file descrip-
Functions: fcntl(2), getmsg(2), poll(2), putmsg(2), read(2), select(2), write(2), getdtablesize(2)
Standards: standards(5) delim off