create descriptor pair for interprocess communication
Standard C Library (libc, -lc)
pipe() function creates a pipe,
which is an object allowing bidirectional data flow, and allocates a pair of
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
pipe() function calls the
pipe2() system call. As a result, system call traces
such as those captured by
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.
calls will fail if:
- fildes argument points to an invalid memory
- 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.
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