pipe - create an interprocess channel
#include <unistd.h> int pipe(int fildes[2]);
The pipe() function creates an I/O mechanism called a pipe and returns two file descriptors, fildes[0] and fildes[1]. The files associated with fildes[0] and fildes[1] are streams and are both opened for reading and writing. The O_NDELAY, O_NONBLOCK, and FD_CLOEXEC flags are cleared on both file descriptors. The fcntl(2) function can be used to set these flags.
A read from fildes[0] accesses the data written to fildes[1] on a first-in-first-out (FIFO) basis and a read from fildes[1] accesses the data written to fildes [0] also on a FIFO basis.
Upon successful completion pipe() marks for update the st_atime, st_ctime, and st_mtime fields of the pipe.
Upon successful completion, 0 is returned. Otherwise, −1 is returned and errno is set to indicate the error.
The pipe() function will fail if:
More than {OPEN_MAX} file descriptors are already in use by this process.
The number of simultaneously open files in the system would exceed a system-imposed limit.
See attributes(5) for descriptions of the following attributes:
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sh(1), fcntl(2), fstat(2), getmsg(2), poll(2), putmsg(2), read(2), write(2), attributes(5), standards(5), streamio(7I)
Since a pipe is bi-directional, there are two separate flows of data. Therefore, the size (st_size) returned by a call to fstat(2) with argument fildes[ 0] or fildes[1] is the number of bytes available for reading from fildes[0] or fildes[1] respectively. Previously, the size (st_size) returned by a call to fstat() with argument fildes[1] (the write-end) was the number of bytes available for reading from fildes[0] (the read-end).