|PIPE(2)||System Calls Manual||PIPE(2)|
LIBRARY¶Standard C Library (libc, -lc)
pipe() function creates a pipe, which is an object allowing bidirectional data flow, and allocates a pair of file descriptors.
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,
- Set the close-on-exec flag for the new file descriptors.
- 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
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 appears on (i.e., can be read from) fildes. 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.
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
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.
pipe2() system calls will fail if:
- fildes argument points to an invalid memory location.
- Too many descriptors are active.
- The system file table is full.
- Not enough kernel memory to establish a pipe.
pipe2() system call will also fail
- The flags argument is invalid.
SEE ALSO¶sh(1), fork(2), read(2), socketpair(2), write(2)
pipe() function appeared in Version 3 AT&T UNIX.
Bidirectional pipes were first used on AT&T System V Release 4 UNIX.
pipe2() function appeared in
pipe() function became a wrapper
pipe2() in FreeBSD
|December 1, 2017||Linux 4.19.0-13-amd64|